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BARBARA  COLLEGE  LIBRARf 


WALKIVO,  SWIMMIXO,  AXD  FLYING. 


THE  INTERNATIONAL  SCIENTIFIC  SERIES. 


ANIMAL    LOCOMOTION 


WALKING,  SWIMMING,  AND  FLYING, 


WITH  A  DISSERTATION  ON 


AERONAUTICS. 


BY 

J.  BELL  PETTIGREW,  M.D.  F.R.S.  F.R.S.E.  F.R.C.P.E. 

PATHOLOGIST  TO   THE    ROYAL    INFIRMARY   OF  EDINBURGH  ',    CURATOR    OF    THE    JIU6EUM   OF  THE 
ROYAX,  COLLEGE  OF  SURGEONS  OF  EDINBURGH  ; 

Extraordinary   Member  and    late  President  of  the  Royal  Medical  Society  of   Edinburgh ;  Croonian  Lecturer 

to  the  Royal  Society' of  London  for  1860 ;  Lecturer  to  the  Royal  Institution  of  Great  Britain  and 

Russell  Institution,  1867  ;  Lecturer  to  the  Royal  College  of  Surgeons  of  Edinburgh, 

1872  ;  Author  of  numerous  Memoirs  on  Physiological  Subjects  in  the 

Philosophical  aiid  other  Transactions,  etc.  etc.  etc. 


ILLUSTRATED  BY  130  ENGRAVINGS  ON  WOOD. 


NEW  YORK: 
D.    APPLETON    &    COMPANY, 

549    &    551    BROADWAY. 

1874. 


PREFACE. 

IN  the  present  volume  I  have  endeavoured  to  explain, 
in  simple  language,  some  difficult  problems  in  "  Animal 
Mechanics."  In  order  to  avoid  elaborate  descriptions,  I 
have  introduced  a  large  number  of  original  Drawings 
and  Diagrams,  copied  for  the  most  part  from  my  Papers 
and  Memoirs  "  On  Flight,"  and  other  forms  of  "  Animal 
Progression."  I  have  drawn  from  the  same  sources 
many  of  the  facts  to  be  found  in  the  present  work.  My 
best  thanks  are  due  to  Mr.  W.  Ballingall,  of  Edinburgh, 
for  the  highly  artistic  and  effective  manner  in  which  he 
has  engraved  the  several  subjects.  The  figures,  I  am 
happy  to  state,  have  in  no  way  deteriorated  in  his 
hands. 


ROYAL  COLLEGE  OP  SURGEONS  OF  EDINBURGH, 
July  1873. 


CONTENTS. 


ANIMAL   LOCOMOTION. 

INTRODUCTION. 

MM 

Motion  associated  with  the  life  and  well-being  of  animals,        .  1 

Motion  not  confined  to  the  animal   kingdom ;  all  matter  in 
motion ;  natural   and    artificial  motion ;    the  locomotive, 
steamboat,  etc.     A  flying  machine  possible,  .  .  2 

Weight  necessary  to  flight,         .....  3 

The  same  laws  regulate  natural  and  artificial  progression,          .  4 

Walking,  swimming,  and  flying  correlated,        ...  5 

Flight  the  poetry  of  motion,       .....  6 

Flight  a  more  unstable  movement  than  that  of  walking  and 
swimming ;  the  travelling  surfaces  and  movements  of  ani- 
mals adapted  to  the  earth,  the  water,  and  the  air,  .  7 
The  earth,  the  water,  and  the  air  furnish  the  fulcra  for  the  levers 

formed  by  the  travelling  surfaces  of  animals,          .  .  8 

Weight  plays  an  important  part  in  walking,  swimming,  and 

flying,          .  .  9 

The  extremities  of  animals  in  walking  act  as  pendulums,  and 

describe  figure-of-8  curves,  ....  9 

In  swimming,  the  body  of  the  fish  is  thrown  into  figure-of-8 

curves,       .  .  .  .  .  .  .10 

The  tail  of  the  fish  made  to  vibrate  pendulum  fashion,  .          1 1 

The  tail  of  the  fish,  the  wing  of  the  bird,  and  the  extremity  of 
the  biped  and  quadruped  are  screws  structurally  and 
functionally.  They  describe  figure-of-S  and  waved  tracks,  12 


vi  CONTENTS. 

PAGE 

The  body  and  wing  reciprocate  in  flight ;  the  body  rising  when 

the  wing  is  falling,  and  vice  versd,  .  .  .12 

Flight  the  least  fatiguing  kind  of  motion.     Aerial  creatures  not 
stronger  than  terrestrial  ones,         .  .  .  • 

Fins,  flippers,  and  wings  form  mobile  helics  or  screws,  .          14 

Artificial  fins,  flippers,  and  wings  adapted  for  navigating  the 

water  and  air,         ......         14 

History  of  the  figure-of-8  theory  of  walking,  swimming,  and 

flying,         .......         15 

Priority  of  discovery  on  the  part  of  the  Author.     Admission  to 

that  effect  on  the  part  of  Professor  Marey,  .  .          16 

Fundamental  axioms.     Of  uniform  motion.     Motion  uniformly 

varied,         .  .  .  .  .  .  .17 

The  legs  move  by  the  force  of  gravity.     Resistance  of  fluids. 
Mechanical  effects  of  fluids  on  animals  immersed  in  them. 
Centre  of  gravity,   .  .  .  •  •  •          18 

The  three  orders  of  lever,  .  .  V  .  .         19 

Passive  organs  of  locomotion.     Bones,  .  .  .  .21 

Joints,    .  .  .  .  .  .  .  .23 

Ligaments.     Effects  of  atmospheric  pressure  on  limbs.     Active 
organs  of  locomotion.    Muscles ;  their  properties,  arrange- 
ment, modes  of  action,  etc.,  .  .  .24 
Muscular   cycles.     Centripetal  and  centrifugal   movements  of 
muscles ;  muscular  waves.     Muscles  arranged  in  longitu- 
dinal, transverse,  and  oblique  spiral  lines,               .              .    2b-27 
The  bones  of  the  extremities  twisted  and  spiral,             .             .         28 
Muscles  take  precedence  of  bones  in  animal  movements,             .         29 
Oblique  spiral  muscles  necessary  for  spiral  bones  and  joints,     .         3] 
The  spiral  movements  of  the  spine  transferred  to  the  extremi- 
ties, 00 

•  •  .  oo 

The   travelling  surfaces   of    animals  variously   modified    and 

adapted  to  the  media  on  or  in  which  they  move,   .  .    34-36 


PROGRESSION  ON  THE  LAND. 

Walking  of  the  Quadruped,  Biped,  etc.,  .  .  37 

Locomotion  of  the  Horse, 

.  O  J 

Locomotion  of  the  Ostrich,         .  AK 

Locomotion  of  Man,  .  .  r. 


CONTENTS.  vii 


PAGE 

Swimming  of  the  Fish,  Whale,  Porpoise,  etc.,    .  .  .66 

Swimming  of  the  Seal,  Sea-Bear,  and  Walrus,   .  .  .74 

Swimming  of  Man,         ......         78 

Swimming  of  the  Turtle,  Triton,  Crocodile,  etc.,  .  .         89 

Flight  under  water,        ......         90 

Difference  between  sub-aquatic  and  aerial  flight,  .  .         92 

Flight  of  the  Flying-fish ;  the  kite-like  action  of  the  wings,      .         98 


PROGRESSION  IN  OR  THROUGH  THE  AIR. 

The  wing  a  lever  of  the  third  order,  .  .  .  .  103 

Weight  necessary  to  flight,  .  .  .  .  .110 

Weight  contributes  to  horizontal  flight,  .  .  .  112 

Weight,  momentum  and  power  to  a  certain  extent  synonymous 

in  flight,  .  .  .  .  .  114 

Air-cells  in  insects  and  birds  not  necessary  to  flight,  .  .115 

How  balancing  is  effected  in  flight,  .  .  .  .118 

Rapidity  of  wing  movements  partly  accounted  for,  .  .  120 

The  wing  area  variable  and  in  excess,  .  .  .  .124 

The  wing  area  decreases  as  the  size  and  weight  of  the  volant 

animal  increases,     .  .  .  .  .  .132 

Wings,  their  form,  etc.  All  wings  screws,  structurally  and 

functionally,  .  .  .  .  .  .136 

The  wing,  during  its  action,  reverses  its  planes,  and  describes 

a  figure-of-8  track  in  space,  ....  140 

The  wing,  when  advancing  with  the  body,  describes  a  looped 

and  waved  track,    .  .  .  .  .  .143 

The  margins  of  the  wing,  thrown  into  opposite  curves  during 

extension  and  flexion,  .....  146 
The  tip  of  the  bat  and  bird's  wing  describes  an  ellipse,  .  147 

The  wing  capable  of  change  of  form  in  all  its  parts,  .  .  147 

The  wing  during  its  vibration  produces  a  cross  pulsation,  .  148 
Compound  rotation  of  the  wing,  .  .  .  .149 

The  wing  vibrates  unequally  with  reference  to  a  given  line,  .  150 
Points  wherein  the  screws  formed  by  the  wings  differ  from 

those  in  common  use,          .  .  .  .  .15] 


viii  CONTENTS. 

PAGE 

The  wing  at  all  times  thoroughly  under  control,  .  .  154 
The  natural  wing  when  elevated  and  depressed  must  move  for- 

Weird  s  •  •  •  •  J.QU 

The  wing  ascends  when  the  body  descends,  and  vice  versd,  .  159 
The  wing  acts  upon  yielding  fulcra,  .  .  .  .  .165 
The  wing  acts  as  a  true  kite  both  during  the  down  and  up 

strokes,  .  .  .  .  •  -.  .  •  165 

Where  the  kite  formed  by  the  wing  differs  from  the  boy's  kite,  166 

The  angles  formed  by  the  wing  during  its  vibrations,  .  .  167 

The  body  and  wings  move  in  opposite  curves,  .  .  .  168 


THE  WINGS  OF  INSECTS,  BATS,  AND  BIRDS. 

Elytra  or  wing  cases  and  membranous  wings ;  their  shape  and 

uses,  ...  170 


THE  WINGS  OF  BATS. 

The  bones  of  the  wing  of  the  bat ;  the  spiral  configuration  of 

their  articular  surfaces,      ...  176 


THE  WINGS  OF  BIRDS. 

The  bones  of  the  wing  of  the  bird ;  their  articular  surfaces, 

movements,  etc.,  .  jijg 

Traces  of  design  in  the  wing  of  the  bird;  the  arrangement  of 

the  primary,  secondary,  and  tertiary  feathers,  etc.,  .  180 

The  wing  of  the  bird  not  always  opened  up  to  the  same  extent 

in  the  up  stroke,  .  jg2 

Flexion  of  the  wing  necessary  to  the  flight  of  birds,      .'  .'       183 

Consideration  of  the  forces  which  propel  the  wings  of  insects,  .       186 
Speed  attained  by  insects,          .  '  TOO 

Consideration  of  the  forces  which  propel  the  wings  of  bats  and 
birds, 

Lax  condition  of  the  shoulder-joint  in  bats  and  birds,  ' 
The  wmg  flexed  and  partly  elevated  by  the  action  of  elastic 
igaments;  the  nature  and  position  of  said  ligaments  in 

Pheasant,  Snipe,  Crested  Crane,  Swan,  etc,  19, 


CONTENTS.  IX 

PAGE 

The  elastic  ligaments  more  highly  differentiated  in  wings  which 

vibrate  rapidly,       .  .  .  .  .  .193 

Power  of  the  wing,  to  what  owing,         .  .  .  .194 

Reasons  why  the   effective  stroke  should  be  delivered  down- 
wards and  forwards,  .  .  .  .  .195 

The  wing  acts  as  an  elevator,  propeller,  and  sustainer,  both 

during  extension  and  flexion,  .  .  .  .197 

Flight  divisible  into  four  kinds,  ....       197 

The  flight  of  the  Albatross  compared  to  the  movements  of  a 

compass  set  upon  gimbals,  .  .  .  .199 

The  regular  and  irregular  in  flight,        .  .  .  .201 

Mode  of  ascending,  descending,  turning,  etc.,    .  .  .       201 

The  flight  of  birds  referable  to  muscular  exertion  and  weight,  .       204 
Lifting  capacity  of  birds,  .  .  .  .  .       205 


AERONAUTICS. 

The  balloon,       .......       210 

The  inclined  plane,         .  .  .  .  .  .211 

The  aerial  screw,  .  .  .  .  .  .215 

Artificial  wings  (Borelli's  views),  ....       219 

Marey's  views,  .  .  .  .  .  .  .226 

Chabrier's  views,  .  ....       233 

Straus-Durckheim's  views,         .....       233 

The  Author's  views ;  his  method  of  constructing  and  applying 
artificial  wings,  as  contra-distinguished  from  that  of  Borelli, 
Chabrier,  Durckheim,  and  Marey,  .  .  .       235 

The  wave  wing  of  the  Author,  ....       236 

How  to  construct  an  artificial  wave  wing  on  the  insect  type,    .       240 
How  to  construct  a  wave  wing  which  shall  evade  the  super- 
imposed air  during  the  up  stroke,  ....       241 

Compound  wave  wing  of  the  Author,    .  .  .  .       242 

How  to  apply  artificial  wings  to  the  air,  .  .  .       245 

As  to  the  nature  of  the  forces  required  for  propelling  artificial 

wings,         .......       246 


X  CONTENTS. 

PAGE 

Necessity  for  supplying  the  roots  of  artificial  wings  with  elastic 
structures  in  imitation  of  the  muscles  and  elastic  ligaments 
of  flying  animals,  .  i  •"  .  .  •  .  .  247 

The  artificial  wave  wing  can  be  driven  at  any  speed — it  can 

make  its  own  currents  or  utilize  existing  ones,       .  .251 

Compound  rotation  of  the  artificial  wave  wing.     The  different 

parts  of  the  wing  travel  at  different  speeds,  .  .        252 

How  the  wave  wiug  creates  currents  and  rises  upon  them,  and 

how  the  air  assists  in  elevating  the  wing,  .  .       253 

The  artificial  wing  propelled  at  various  degrees  of  speed  during 

the  down  and  up  strokes,  .....       255 
The  artificial  wave  wing  as  a  propeller,  .  .  .       256 

A  new  form  of  aerial  screw,        .  .  .  .  .        256 

The  aerial  wave  screw  operates  upon  water,      .  .  .       257 

The  sculling  action  of  the  wing,  .  .  .    '          .231 

CONCLUDING  REMARKS,  ....  258 


LIST  OF  ILLUSTRATIONS. 


The  Engravings  are,  with  few  exceptions,  from  Photographs,  Drawings,  and 
Designs  by  Mr.  Charles  Berjeau  and  the  Author.    Such  as  are  not  original 
are  duly  acknowledged. 

PAGE 

FRONTISPIECE. 

In  the  clutch  of  the  enemy — (The  Graphic). 

The  three  orders  of  lever — (Bishop),      .  .  ,  .  19,  20 

The  skeleton  of  a  Deer — (Pander  and  D' Alton),  .  .         21 

Muscular  cycle  in  the  act  of  flexing  the  arm,     .  .  .25 

Screws  formed  by  the  bones  of  the  wing  of  the  bird,  the  bones  of 
the  anterior  extremity  of  the  Elephant,  and  the  cast  of  the 
interior  of  the  left  ventricle  of  the  heart,   .  .  .28 

The  muscular  system  of  the  Horse — (Bagg),      .  .  .30 

The  feet  of  the  Deer,  Ornithorhynchus,  Otter,  Frog,  and  Seal,  .         34 
The  Red-throated  Dragon,          .  .  .  .  .35 

The  Flying  Lemur,         ......         35 

The  Bat,  .......         36 

Chillingham  Bull  with  extremities  describing  figure-of-8  move- 
ments,        .......         37 

Double  waved  tracks  described  by  Man  in  walking,      .  .         39 

Horse  in  the  act  of  trotting,       .  .  .  .  .41 

Footprints  of  the  Horse  in  the  walk,  trot,  and  gallop — (Gamgee),         43 
Skeleton  of  the  Ostrich — (Dallas),          .  .  .  .47 

Ostriches  pursued  by  a  hunter,  .  .  .  .48 

Skeleton  of  Man,  .  .  .  .  .  .55 

The  positions  assumed  by  the  extremities  and  feet  in  walking 

— (Weber)  .  ...  .  .  .  .59 

Preparing  to  run — (Flaxman),  .  .  .  .62 

The  skeleton  of  a  Perch — (Dallas),         .  .  .  .65 

The  Salmon  swimming  leisurely,  .  .  .  .65 

Swimming  of  the  fish  according  to  Borelli,         ...  .67 

Swimming  of  the  fish  according  to  the  Author,  .  .         68 


xij  LIST  OF  ILLUSTRATIONS. 

PAGE 
no 

The  Poipoise  and  Manatee,        ...» 

The  skeleton  of  the  Dugong — (Dallas), 

The  Seal,  ....•••         74 

The  Sea-Bear,    .  • 

The  elliptical,  looped,  and  spiral  tracks  made  in  swimming,      .         81 

The  several  attitudes  assumed  by  the  extremities  in  swimming 

•  •  &2 

in  the  prone  position,          . 

Overhand  swimming,     .  .  •  • 

Side  swimming,  ....«• 

Swimming  of  the  Turtle  and  Triton,      .  .  •  .89 

Swimming  of  the  Little  Penguin,  • 

Sub-aquatic  flight  or  diving,  ..... 
The  feet  of  the  Swan  as  seen  in  the  open  and  closed  condition,  96 
The  foot  of  the  Grebe  with  swimming  membrane — (Dallas),  .  97 
Double  waved  track  described  by  the  feet  of  swimming  birds, .  97 
The  flight  of  the  Flying-fish,  .....  98 
The  wing  a  lever  of  the  third  order,  ....  105 
Figure-of-8  vertical  track  made  by  the  wing  in  flight,  .  .107 

Do.         horizontal  track,      .....       108 
Feathers  and  cork  flying  forward,          .  .  .  .112 

Diagram  illustrating  how  wings  obtain  their  high  speed,  .       120 

Butterfly  with  large  wings,        .  .  .  .  .124 

Beetle  with  small  wings,  .....       125 

Partridge  with  small  wings;  Heron  with  large  wings,  .       126 

The  wings  of  the  Hawk  and  Albatross,          '    .  .  136,  137 

The  Green  Plover  with  one  wing  flexed  and  the  other  extended,       138 
Blur  or  impression  produced  on  the  eye  by  the  rapidly  oscillat- 
ing wing  of  the  insect,        .  .  .  .  .139 
Diagram  in  which  the  down  and  up  strokes  of  the  wing  of  the 

insect  are  analysed,  .....       141 

Diagrams  illustrating  the  looped  and  waved  tracks  described 

by  the  wing  of  the  insect,  bat,  and  bird,    .  .  .       144 

Figures  showing  the  positions  assumed  by  the  wing  of  the  bird 

during  the  up  and  down  strokes  (side  view),     *    .         . :  •       145 
The  positions  assumed  by  the  wing  of  the  insect  as  it  hastens 

to  and  fro  and  describes  a  figure-of-8  track,  . ".          .       141 

The  figure-of-8  curves  made  by  the  wing  of  the  bird  in  flexion 

antl  extension,        ....  .        147 

The  longSiud  short  axes  of  the  wing,     .  .  .  .149 

The  waved  tracks  described  by  the  wing  and  body  of  the  bird 

as  they  alternately  rise  and  fall,     .  .  .  157, 163 


LIST  OF  ILLUSTRATIONS.  xiii 

PAGK 

The  positions  assumed  by  the  wing  of  the  bird  during  the 

down  and  up  strokes  (front  view),  .  ^  .       158 

Analysis  of  the  movements  of  the  wing,  .  .  160, 161 

The  kite-like  action  and  waved  movements  of  the  wing,  .       166 

The  Centaur  Beetle  and  Water  Bug,      .  .  .  .171 

The  Dragon  Fly,  .  .  .  .  .  .172 

The  screws  formed  by  the  wing  of  the  insect,  bat,  and  bird,  174,  175, 176 
The  muscles,  elastic  ligaments,  and  feathers  of  the  wing  of  the 

bird,  .  ...  .  .  .  .181 

The  flight  of  the  King-fisher,     .  .  .  .  .183 

The  flight  of  the  Gull,  .  .  .  .  .  .186 

The  flight  of  the  Owl,    .  .  .  .  .  .198 

The  flight  of  the  Albatross,         .  .  .  .  .       200 

Pigeon  and  Duck  alighting,      . .  .  .  .  203,  204 

Hawk  and  quarry — (The  Graphic),         .  .  .  .       206 

The  Vauxhall  Balloon  of  Mr.  Green,      .  .  .  .208 

Mr.  Henson's  Flying  Machine,  .  .  .  .  .212 

Mr.  Stringfellow's  Flying  Machine,        ....       213 

Sir  George  Cayley's  Flying  Apparatus,  .  .  .       215 

Flying  Machine  designed  by  De  la  Landelle,      .  .  21 'JB 

Borelli's  Artificial  Bird,  .  .  .  .  .220 

Diagrams  illustrating  the  true  and  false  action  of  the  wing,      .       228 
The  sculling  action  of  the  wing  as  seen  in  the  bird,       .  .231 

The  artificial  wave  wing  of  the  Author,  .  ...       237 

Do.  do.  with  driving  apparatus,  .  .       239 

Various  forms  of  artificial  wings  by  the  Author,  .  .       241 

The  compound  wave  wing  of  the  Author,          .  .  .       243 

Diagrams  illustrative  of  artificial  wing  movements,       .          •    .       250 
Diagram  illustrating  the  currents  produced  by  the  movements 

of  artificial  wings,  ......       253 

The  aerial  wave  screw  of  the  Author,    ....       256 

Swallow  in  pursuit  of  insects,    .  .  .  .         -    .       260 


ANIMAL    LOCOMOTION. 


ANIMAL   LOCOMOTION. 


INTRODUCTION". 

THE  locomotion  of  animals,  as  exemplified  in  walking,  swim- 
ming, and  flying,  is  a  subject  of  permanent  interest  to  all 
who  seek  to  trace  in  the  creature  proofs  of  beneficence  and 
design  in  the  Creator.  All  animals,  however  insignificant,  have 
a  mission  to  perform — a  destiny  to  fulfil ;  and  their  manner  of 
doing  it  cannot  be  a  matter  of  indifference,  even  to  a  careless 
observer.  The  most  exquisite  form  loses  much  of  its  grace 
if  bereft  of  motion,  and  the  most  ungainly  animal  conceals  its 
want  of  symmetry  in  the  co-adaptation  and  exercise  of  its 
several  parts.  The  rigidity  and  stillness  of  death  alone  are 
unnatural.  So  long  as  things  "  live,  move,  and  have  a  being," 
they  are  agreeable  objects  in  the  landscape.  They  are  part 
and  parcel  of  the  great  problem  of  life,  and  as  we  are  all 
hastening  towards  a  common  goal,  it  is  but  natural  we  should 
take  an  interest  in  the  movements  of  our  fellow-travellers. 
As  the  locomotion  of  animals  is  intimately  associated  withl 
their  habits  and  modes  of  life,  a  wide  field  is  opened  up, 
teeming  with  incident,  instruction,  and  amusement.  No  one_J 
can  see  a  bee  steering  its  course  with  admirable  precision  from 
flower  to  flower  in  search  of  nectar ;  or  a  swallow  darting 
like  a  flash  of  light  along  the  lanes  in  pursuit  of  insects  ;  or 
a  wolf  panting  in  breathless  haste  after  a  deer  ;  or  a  dolphin 
rolling  like  a  mill-wheel  after  a  shoal  of  flying  fish,  without 
feeling  his  interest  keenly  awakened. 


2  ANIMAL  LOCOMOTION. 

Nor  is  this  love  of  motion  confined  to  the  animal  kingdom. 
We  admire  a  cataract  more  than  a  canal ;  the  sea  is  grander 
in  a  hurricane  than  in  a  calm ;  and  the  fleecy  clouds  which 
constantly  flit  overhead  are  more  agreeable  to  the  eye  than 
a  horizon  of  tranquil  blue,  however  deep  and  beautiful.  We 
never  tire  of  sunshine  and  shadow  when  together  :  we  readily 
tire  of  either  by  itself.  Inorganic  changes  and  movements 
are  scarcely  less  interesting  than  organic  ones.  The  disaffected 
growl  of  the  thunder,  and  the  ghastly  lightning  flash,  scorching 
and  withering  whatever  it  touches,  forcibly  remind  us  that 
everything  above,  below,  and  around  is  in  motion.  Of  ab- 
solute rest,  as  Mr.  Grove  eloquently  puts  it,  nature  gives  us 
no  evidence.  All  matter,  whether  living  or  dead,  whether 
solid,  liquid,  or  gaseous,  is  constantly  changing  form  :  in  other 
words,  is  constantly  moving.  It  is  well  it  is  so ;  for  those 
incessant  changes  in  inorganic  matter  and  living  organisms 
introduce  that  fascinating  variety  which  palls  not  upon  the 
eye,  the  ear,  the  touch,  the  taste,  or  the  smell.  If  an  absolute 
repose  everywhere  prevailed,  and  plants  and  animals  ceased  to 
grow ;  if  day  ceased  to  alternate  with  night  and  the  fountains 
were  dried  up  or  frozen;  if  the  shadows  refused  to  creep,  the  air 
and  rocks  to  reverberate,  the  clouds  to  drift,  and  the  great  race 
of  created  beings  to  move,  the  world  would  be  no  fitting  habi- 
tation for  man.  In  change  he  finds  his  present  solace  and 
future  hope.  The  great  panorama  of  life  is  interesting  be- 
cause it  moves.  One  change  involves  another,  and  every- 
thing which  co-exists,  co-depends.  This  co-existence  and 
inter-dependence  causes  us  not  only  to  study  ourselves,  but 
everything  around  us.  By  discovering  natural  laws  we  are 
permitted  in  God's  good  providence  to  harness  and  yoke 
natural  powers,  and  already  the  giant  Steam  drags  along  at 
incredible  speed  the  rumbling  car  and  swiftly  gliding  boat ; 
the  quadruped  has  been  literally  outraced  on  the  land,  and  the 
ish  in  the  sea;  each  has  been,  so  to  speak,  beaten  in  its  own 
That  the  tramway  of  the  air  may  and  wiU  be  tra- 
il by  man's  ingenuity  at  some  period  or  other,  is,  reasoning 

om  analogy  and  the  nature  of  things,  equally  certain.  If 
there  were  no  flying  things-if  there  were  no  insects,  bats, 
or  birds  as  models,  artificial  flight  (such  are  the  difficulties 


INTRODUCTION.  3 

attending  its  realization)  might  well  be  regarded  an  impossi- 
bility. As,  however,  the  flying  creatures  are  lesion,  both  as 
regards  number,  size,  and  pattern,  and  as  the  bodies  of  all  are 
not  only  manifestly  heavier  than  the  air,  but  are  composed 
of  hard  and  soft  parts,  similar  in  all  respects  to  those  com- 
posing the  bodies  of  the  other  members  of  the  animal  kingdom, 
we  are  challenged  to  imitate  the  movements  of  the  insect,  bat, 
and  bird  in  the  air,  as  we  have  already  imitated  the  move- 
ments of  the  quadruped  on  the  land  and  the  fish  in  the  water. 
We  have  made  two  successful  steps,  and  have  only  to  make 
a  third  to  complete  that  wonderfully  perfect  and  very  com- 
prehensive system  of  locomotion  which  we  behold  in  nature. 
Until  this  third  step  is  taken,  our  artificial  appliances  for 
transit  can  only  be  considered  imperfect  and  partial.  Those 
authors  who  regard  artificial  flight  as  impracticable  sagely 
remark  that  the  land  supports  the  quadruped  and  the  water  the 
fish.  This  is  quite  true,  but  it  is  equally  true  that  the  air  sup- 
ports the  bird,  and  that  the  evolutions  of  the  bird  on  the  wing 
are  quite  as  safe  and  infinitely  more  rapid  and  beautiful  than  the 
movements  of  either  the  quadruped  on  the  land  or  the  fish  in 
the  water.  What,  in  fact,  secures  the  position  of  the  quadruped 
on  the  land,  the  fish  in  the  water,  and  the  bird  in  the  air,  is 
the  life ;  and  by  this  I  mean  that  prime  moving  or  self-govern- 
ing power  which  co-ordinates  the  movements  of  the  travelling 
surfaces  (whether  feet,  fins,  or  wings)  of  all  animals,  and  adapts 
them  to  the  medium  on  which  they  are  destined  to  operate, 
whether  this  be  the  comparatively  unyielding  earth,  the  mobile 
water,  or  the  still  more  mobile  air.  Take  away  this  life  suddenly 
— the  quadruped  falls  downwards,  the  fish  (if  it  be  not  speci- 
ally provided  with  a  swimming  bladder)  sinks,  and  the  bird 
gravitates  of  necessity.  There  is  a  sudden  subsiding  and  ces- 
sation of  motion  in  either  case,  but  the  quadruped  and  fish  have 
no  advantage  over  the  bird  in  this  respect.  The  savans  who 
oppose  this  view  exclaim  not  unnaturally  that  there  is  no 
great  difficulty  in  propelling  a  machine  either  along  the  lard 
or  the  water,  seeing  that  both  these  media  support  it.  There 
is,  I  admit,  no  great  difficulty  now,  but  there  were  apparently 
insuperable  difficulties  before  the  locomotive  and  steam-boat 
were  ir.  vented.  Weight,  moreover,  instead  of  being  a  barrier  to 


4  ANIMAL  LOCOMOTION. 

artificial  flight  is  absolutely  necessary  to  it.  This  statement 
is  quite  opposed  to  the  commonly  received  opinion,  but  is 
nevertheless  true.  No  bird  is  lighter  than  the  air,  and  no 
machine  constructed  to  navigate  it  should  aim  at  being  specifi- 
cally lighter.  What  is  wanted  is  a  reasonable  but  not  cumbrous 
amount  of  weight,  and  a  duplicate  (in  principle  if  not  in  prac- 
tice) of  those  structures  and  movements  which  enable  insect?, 
bats,  and  birds  to  fly.  Until  the  structure  and  uses  of  wings 
are  understood,  the  way  of  "  an  eagle  in  the  air  "  must  of  ne- 
cessity remain  a  mystery.  The  subject  of  flight  has  never, 
until  quite  recently,  been  investigated  systematically  or 
rationally,  and,  as  a  result,  very  little  is  known  of  the  laws 
which  regulate  it.  If  these  laws  were  understood,  and  we 
were  in  possession  of  trustworthy  data  for  our  guidance  in 
devising  artificial  pinions,  the  formidable  Gordian  knot  of 
flight,  there  is  reason  to  believe,  could  be  readily  untied. 

That  artificial  flight  is  a  possible  thing  is  proved  beyond 
doubt — 1st,  by  the  fact  that  flight  is  a  natural  movement ; 
and  2d,  because  the  natural  movements  of  walking  and  swim- 
ming have  already  been  successfully  imitated. 

The  very  obvious  bearing  which  natural  movements  have 
upon  artificial  ones,  and  the  relation  which  exists  between 
organic  and  inorganic  movements,  invest  our  subject  with  a 
peculiar  interest 

It  is  the  blending  of  natural  and  artificial  progression  in 
theory  and  practice  which  gives  to  the  one  and  the  other  its 
chief  charm.  The  history  of  artificial  progression  is  essen- 
tially that  of  natural  progression.  The  same  laws  regulate 
and  determine  both.  The  wheel  of  the  locomotive  and  the 
screw  of  the  steam-ship  apparently  greatly  differ  from  the 
limb  of  the  quadruped,  the  fin  of  the  fish,  and  the  wing  of 
the  bird ;  but,  as  I  shall  show  in  the  sequel,  the  curves  which 
go  to  form  the  wheel  and  the  screw  are  found  in  the  travelling 
surfaces  of  all  animals,  whether  they  be  limbs  (furnished  with 
feet),  or  fins,  or  wings. 

It  is  a  remarkable  circumstance  that  the  undulation  or 
wave  made  by  the  wing  of  an  insect,  bat,  or  bird,  when  those 
animals  are  fixed  or  hovering  before  an  object,  and  when  they 
are  flying,  corresponds  in  a  marked  manner  with  the  track 


INTRODUCTION.  5 

described  by  the  stationary  and  progressive  waves  in  fluids, 
and  likewise  with  the  waves  of  sound.  This  coincidence 
would  seem  to  argue  an  intimate  relation  between  the  instru- 
ment and  the  medium  on  which  it  is  destined  to  operate — 
the  wing  acting  in  those  very  curves  into  which  the  atmo- 
sphere is  naturally  thrown  in  the  transmission  of  sound.  Can 
it  be  that  the  animate  and  inanimate  world  reciprocate,  and 
that  animal  bodies  are  made  to  impress  the  inanimate  in  pre- 
cisely the  same  manner  as  the  inanimate  impress  each  other] 
This  much  seems  certain : — The  wind  communicates  to  the 
water  similar  impulses  to  those  communicated  to  it  by  the 
fish  in  swimming ;  and  the  wing  in  its  vibrations  impinges 
upon  the  air  as  an  ordinary  sound  does.  The  extremities  of 
quadrupeds,  moreover,  describe  waved  tracks  on  the  land 
when  walking  and  running ;  so  that  one  great  law  apparently 
determines  the  course  of  the  insect  in  the  air,  the  fish  in  the 
water,  and  the  quadruped  on  the  land. 

We  are,  unfortunately,  not  taught  to  regard  the  travelling 
surfaces  and  movements  of  animals  as  con-elated  in  any 
way  to  surrounding  media,  and,  as  a  consequence,  are  apt 
to  consider  walking  as  distinct  from  swimming,  and  walk- 
ing and  swimming  as  distinct  from  flying,  than  which  there 
can  be  no  greater  mistake.  Walking,  swimming,  and  flying 
are  in  reality  only  modifications  of  eacli  other.  Walk- 
ing merges  into  swimming,  and  swimming  into  flying,  by 
insensible  gradations.  The  modifications  which  result  in 
walking,  swimming,  and  flying  are  necessitated  by  the  fact 
that  the  earth  affords  a  greater  amount  of  support  than  the 
v  water,  and  the  water  than  the  air. 

That  walking,  swimming,  and  flying  represent  integral 
parts  of  the  same  problem  is  proved  by  the  fact  that  most 
quadrupeds  swim  as  well  as  walk,  and  some  even  fly ;  while 
many  marine  animals  walk  as  well  as  swim,  and  birds  and 
insects  walk,  swim,  and  fly  indiscriminately.  When  the  land 
animals,  properly  so  called,  are  in  the  habit  of  taking  to  the 
water  or  the  air;  or  the  inhabitants  of  the  water  are  constantly 
taking  to  the  land  or  the  air ;  or  the  insects  and  birds  which 
are  more  peculiarly  organized  for  flight,  spend  much  of  their 
time  on  the  land  and  in  the  water ;  their  organs  of  locomo- 


6  ANIMAL  LOCOMOTION. 

tion  must  possess  those  peculiarities  of  structure  which  charac- 
terize, as  a  class,  those  animals  which  live  on  the  land,  in 
the  water,  or  in  the  air  respectively. 

In  this  we  have  an  explanation  of  the  gossamer  wing  of 
the  insect, — the  curiously  modified  hand  of  the  bat  and  bird, 
—the  webbed  hands  and  feet  of  the  Otter,  Ornithorhynchus, 
Seal,  and  Walrus,— the  expanded  tail  of  the  Whale,  Porpoise, 
Dugong,  and  Manatee,— the  feet  of  the  Ostrich,  Apteryx,  and 
Dodo,  exclusively  designed  for  running, — the  feet  of  the 
Ducks,  Gulls,  and  Petrels,  specially  adapted  for  swimming, — 
and  the  wings  and  feet  of  the  Penguins,  Auks,  and  Guille- 
mots, especially  designed  for  diving.  Other  and  intermediate 
modifications  occur  in  the  Flying-fish,  Flying  Lizard,  and 
Flying  Squirrel ;  and  some  animals,  as  the  Frog,  Newt,  and 
several  of  the  aquatic  insects  (the  Ephemera  or  May-fly  for 
example1)  which  begin  their  career  by  swimming,  come 
ultimately  to  walk,  leap,  and  even  fly.2 

Every  degree  and  variety  of  motion,  which  is  peculiar  to 
the  land,  and  to  the  water-  and  air-navigating  animals  as  such, 
is  imitated  by  others  which  take  to  the  elements  in  question 
secondarily  or  at  intervals. 

Of  all  animal  movements,  flight  is  indisputably  the  finest. 
It  may  be  regarded  as  the  poetry  of  motion.  The  fact  that 
a  creature  as  heavy,  bulk  for  bulk,  as  many  solid  substances, 
can  by  the  unaided  movements  of  its  wings  urge  itself  through 

1  The  Ephemerae  in  the  larva  and  pupa  state  reside  in  the  water  concealed 
during  the  day  under  stones  or  in  horizontal  bnrrows  which  they  form  in  the 
banks.  Although  resembling  the  perfect  insect  in  several  respects,  they  differ 
materially  in  having  longer  antennae,  in  wanting  ocelli,  and  in  possessing 
horn-like  mandibles;  the  abdomen  has,  moreover,  on  each  side  a  row  of 
plates,  mostly  in  pairs,  which  are  a  kind  of  false  branchiae,  and  which  are 
employed  not  only  in  respiration,  but  also  as  paddles. — Cuvier's  Animal 
Kingdom,  p.  576.  London,  1840. 

*  Kirby  and  Spence  observe  that  some  insects  which  are  not  naturally 
aquatic,  do,  nevertheless,  swim  very  well  if  they  fall  into  the  water.  They 
instance  a  kind  of  grasshopper  (Acrydium),  which  can  paddle  itself  across  a 
stream  with  great  rapidity  by  the  powerful  strokes  of  its  hind  legs. — (Intro- 
duction to  Entomology,  5th  edit.,  1828,  p.  360.)  Nor  should  the  remarkable 
discovery  by  Sir  John  Lubbock  of  a  swimming  insect  (Polynema  natans), 
which  uses  its  wings  exclusively  as  fins,  be  overlooked.— Linn.  Trans,  vol. 
xxiv.  p.  135. 


INTEODUCTION.  7 

the  air  with  a  speed  little  short  of  a  cannon-ball,  fills  the 
mind  with  wonder.  Flight  (if  I  may  be  allowed  the  expres- 
sion) is  a  more  unstable  movement  than  that  of  walking 
and  swimming ;  the  instability  increasing  as  the  medium  to 
be  traversed  becomes  less  dense.  It,  however,  does  not 
essentially  differ  from  the  other  two,  and  I  shall  be  able  to 
show  in  the  following  pages,  that  the  materials  and  forces 
employed  in  flight  are  literally  the  same  as  those  employed 
in  walking  and  swimming.  This  is  an  encouraging  circum- 
stance as  tar  as  artificial  flight  is  concerned,  as  the  same  ele- 
ments and  forces  employed  in  constructing  locomotives  and 
steamboats  may,  and  probably  will  at  no  distant  period, 
be  successfully  employed  in  constructing  flying  machines. 
Flight  is  a  purely  mechanical  problem.  It  is  warped  in  and 
out  with  the  other  animal  movements,  and  forms  a  link  of  a 
great  chain  of  motion  which  drags  its  weary  length  over  the 
land,  through  the  water,  and,  notwithstanding  its  weight, 
through  the  air.  To  understand  flight,  it  is  necessary  to 
understand  walking  and  swimming,  and  it  is  with  a  view  to 
simplifying  our  conceptions  of  this  most  delightful  form  of 
locomotion  that  the  present  work  is  mainly  written.  The 
chapters  on  walking  and  swimming  naturally  lead  up  to  those 
on  flying. 

In  the  animal  kingdom  the  movements  are  adapted  either 
to  the  land,  the  water,  or  the  air ;  these  constituting  the  three 
great  highways  of  nature.  As  a  result,  the  instruments  by 
which  locomotion  is  effected  are  specially  modified.  This  is 
necessary  because  of  the  different  densities  and  the  different 
degrees  of  resistance  furnished  by  the  land,  water,  and  air 
respectively.  On  the  land  the  extremities  of  animals  en- 
counter the  maximum  of  resistance,  and  occasion  the  minimum 
of  displacement.  In  the  air,  the  pinions  experience  the  mini- 
mum of  resistance,  and  effect  the  maximum  of  displacement;  the 
water  being  intermediate  both  as  regards  the  degree  of 
resistance  offered  and  the  amount  of  displacement  produced. 
The  speed  of  an  animal  is  determined  by  its  shape,  mass, 
power,  and  the  density  of  the  medium  on  or  in  which  it 
moves.  It  is  more  difficult  to  walk  on  sand  or  snow  than  on 
a  macadamized  road.  In  like  manner  (unless  the  travelling 


3  ANIMAL  LOCOMOTION. 

surfaces  are  specially  modified),  it  is  more  troublesome  to 
swim  than  to  walk,  and  to  fly  than  to  swim.  This  arises  from 
the  displacement  produced,  and  the  consequent  want  of  sup- 
port. The  land  supplies  the  fulcrum  for  the  levers  formed 
by  the  extremities  or  travelling  surfaces  of  animals  with 
terrestrial  habits;  the  water  furnishes  the  fulcrum  for  the 
levers  formed  by  the  tail  and  fins  of  fishes,  sea  mammals, 
etc.;  and  the  air  the  fulcrum  for  the  levers  formed  by  the 
wings  of  insects,  bats,  and  birds.  The  fulcrum  supplied  by 
the  land  is  immovable ;  that  supplied  by  the  water  and  air 
movable.  The  mobility  and  immobility  of  the  fulcrum  con- 
stitute the  principal  difference  between  walking,  swimming, 
and  flying ;  the  travelling  surfaces  of  animals  increasing  in 
size  as  the  medium  to  be  traversed  becomes  less  dense  and 
the  fulcrum  more  movable.  Thus  terrestrial  animals  have 
smaller  travelling  surfaces  than  amphibia,  amphibia  than  fishes, 
and  fishes  than  insects,  bats,  and  birds.  Another  point  to  be 
studied  in  connexion  with  unyielding  and  yielding  fulcra,  is 
the  resistance  offered  to  forward  motion.  A  land  animal  is 
supported  by  the  earth,  and  experiences  little  resistance  from 
the  air  through  which  it  moves,  unless  the  speed  attained  is 
high.  Its  principal  friction  is  that  occasioned  by  the  contact 
of  its  travelling  surfaces  with  the  earth.  If  these  are  few,  the 
speed  is  generally  great,  as  in  quadrupeds.  A  fish,  or  sea  mam- 
mal, is  of  nearly  the  same  specific  gravity  as  the  water  it  in- 
habits; in  other  words,  it  is  supported  with  as  little  or  less  effort 
than  a  land  animal.  As,  however,  the  fluid  in  which  it  moves 
is  more  dense  than  air,  the  resistance  it  experiences  in  forward 
motion  is  greater  than  that  experienced  by  land  animals,  and 
by  insects,  bats,  and  birds.  As  a  consequence  fishes  are  for 
the  most  part  elliptical  in  shape ;  this  being  the  form  calcu- 
lated to  cleave  the  water  with  the  greatest  ease.  A  flying 
animal  is  immensely  heavier  than  the  air.  The  support 
which  it  receives,  and  the  resistance  experienced  by  it 
in  forward  motion,  are  reduced  to  a  minimum.  Flight, 
because  of  the  rarity  of  the  air,  is  infinitely  more  rapid  than 
either  walking,  running,  or  swimming.  The  flying  animal 
receives  support  from  the  air  by  increasing  the  size  of  its 
travelling  surfaces,  which  act  after  the  manner  of  twisted 


INTRODUCTION.  9 

inclined  planes  or  kites.  When  an  insect,  a  bat,  or  a  bird 
is  launched  in  space,  its  weight  (from  the  tendency  of  all 
bodies  to  fall  vertically  downwards)  presses  upon  the  inclined 
planes  or  kites  formed  by  the  wings  in  such  a  manner  as 
to  become  converted  directly  into  a  propelling,  and  indirectly 
into  a  buoying  or  supporting  power.  This  can  be  proved  by 
experiment,  as  I  shall  show  subsequently.  But  for  the  share 
which  the  weight  or  mass  of  the  flying  creature  takes  in  flight, 
the  protracted  journeys  of  birds  of  passage  would  be  impos- 
sible. Some  authorities  are  of  opinion  that  birds  even  sleep 
upon  the  wing.  Certain  it  is  that  the  albatross,  that  prince 
of  the  feathered  tribe,  can  sail  about  for  a  whole  hour  without 
once  flapping  his  pinions.  This  can  only  be  done  in  virtue 
of  the  weight  of  the  bird  acting  upon  the  inclined  planes  or 
kites  formed  by  the  wings  as  stated. 

The  weight  of  the  body  plays  an  important  part  in  walking 
and  swimming,  as  well  as  in  flying.  A  biped  which  advances 
by  steps  and  not  by  leaps  may  be  said  to  roll  over  its  extre- 
mities,1 the  foot  of  the  extremity  which  happens  to  be  upon 
the  ground  for  the  time  forming  the  centre  of  a  circle,  the 
radius  of  which  is  described  by  the  trunk  in  forward  motion. 
In  like  manner  the  foot  which  is  off  the  ground  and  swinging 
forward  pendulum  fashion  in  space,  may  be  said  to  roll  or 
rotate  upon  the  trunk,  the  head  of  the  femur  forming  the 
centre  of  a  circle  the  radius  of  which  is  described  by  the  ad- 
vancing foot.  A  double  rolling  movement  is  thus  established, 
the  body  rolling  on  the  extremity  the  one  instant,  the  extre- 
mity rolling  on  the  trunk  the  next.  During  these  movements 
the  body  rises  and  falls.  The  double  rolling  movement  is 
necessary  not  only  to  the  progression  of  bipeds,  but  also  to 
that  of  quadrupeds.  As  the  body  cannot  advance  without 
the  extremities,  so  the  extremities  cannot  advance  without 
the  body.  The  double  rolling  movement  is  necessary  to  con- 
tinuity of  motion.  If  there  was  only  one  movement  there 
•would  be  dead  points  or  halts  in  walking  and  running,  similar 
to  what  occur  in  leaping.  The  continuity  of  movement  neces- 
sary to  progression  in  some  bipeds  (man  for  instance)  is  fur- 

1  This  is  also  true  of  quadrupeds.  It  is  the  posterior  part  of  the  feet 
which  is  set  down  first. 


]  0  ANIMAL  LOCOMOTION. 

th  n*  secured  by  a  pendulum  movement  in  the  arms  as  well  as 
in  the  legs,  the  right  arm  swinging  before  the  body  when  the 
right  leg  swings  behind  it,  and  the  converse.  The  right  leg 
and  left  arm  advance  simultaneously,  and  alternate  with  the 
left  leg  and  right  arm,  which  likewise  advance  together.  This 
gives  rise  to  a  double  twisting  of  the  body  .at  the  shoulders 
and  loins.  The  legs  and  arms  when  advancing  move  in 
curves,  the  convexities  of  the  curves  made  by  the  right  leg 
and  left  arm,  which  advance  together  when  a  step  is  being 
made,  being  directed  outwards,  and  forming,  when  placed 
together,  a  more  or  less  symmetrical  ellipse.  If  the  curves 
formed  by  the  legs  and  arms  respectively  be  united,  they 
form  waved  lines  which  intersect  at  every  step.  This  arises 
from  the  fact  that  the  curves  formed  by  the  right  and  left 
legs  are  found  alternately  on  either  side  of  a  given  line,  the 
same  holding  true  of  the  right  and  left  arms.  Walking  is 
consequently  to  be  regarded  as  the  result  of  a  twisting  diagonal 
movement  in  the  trunk  and  in  the  extremities.  Without  this 
movement,  the  momentum  acquired  by  the  different  portions 
of  the  moving  mass  could  not  be  utilized.  As  the  momentum 
acquired  by  animals  in  walking,  swimming,  and  flying  forms 
an  important  factor  in  those  movements,  it  is  necessary  that 
we  should  have  a  just  conception  of  the  value  to  be  attached 
to  weight  when  in  motion.  In  the  horse  when  walking,  the 
stride  is  something  like  five  feet,  in  trotting  ten  feet,  but  in 
galloping  eighteen  or  more  feet.  The  stride  is  in  fact  deter- 
mined by  the  speed  acquired  by  the  mass  of  the  body  of  the 
horse ;  the  momentum  at  which  the  mass  is  moving  carry- 
ing the  limbs  forward.1 

^Tn  the  swimming  of  the  fish,  the  body  is  thrown  into  double 
or  figure-of-8  curves,  as  in  the  walking  of  the  biped.  The  twist- 
ing of  the  body,  and  the  continuity  of  movement  which  that 
twisting  begets,  reappear.  The  curves  formed  in  the  swimming 

1  "  According  to  Sainbell,  the  celebrated  horse  Eclipse,  when  galloping  at 
liberty,  and  with  its  greatest  speed,  passed  over  the  space  of  twenty-five  feet 
at  each  stride,  which  he  repeated  2^  times  in  a  second,  being  nearly  four 
miles  in  six  minutes  and  two  seconds.  The  race-horse  Flying  Childers  was 
computed  to  have  passed  over  eighty-two  feet  and  a  half  in  a  second,  or  nearly 
a  mile  in  a  minute." 


INTRODUCTION.  11 

of  the  fish  are  never  less  than  two,  a  caudal  and  a  cephalic  one. 
They  may  and  do  exceed  this  number  in  the  long-bodied  fishes. 
The  tail  of  the  fish  is  made  to  vibrate  pendulum  fashion  on 
either  side  of  the  spine,  when  it  is  lashed  to  and  fro  in  the 
act  of  swimming.  It  is  made  to  rotate  upon  one  or  more  of 
the  vertebra?  of  the  spine,  the  vertebra  or  vertebrae  forming 
the  centre  of  a  lemniscate,  which  is  described  by  the  caudal 
fin.  There  is,  therefore,  an  obvious  analogy  between  the  tail 
of  the  fish  and  the  extremity  of  the  biped.  This  is  proved  by 
the  conformation  and  swimming  of  the  seal, — an  animal  in 
which  the  posterior  extremities  are  modified  to  resemble  the 
tail  of  the  fish.  In  the  swimming  of  the  seal  the  hind  legs  are 
applied  to  the  water  by  a  sculling  figure-of-8  motion,  in  the 
same  manner  as  the  tail  of  the  fish.  Similar  remarks  might 
be  made  with  regard  to  the  swimming  of  the  whale,  dugong, 
manatee,  and  porpoise,  sea  mammals,  which  still  more  closely 
resemble  the  fish  in  shape.  The  double  curve  into  which  the 
fish  throws  its  body  in  swimming,  and  which  gives  continuity 
of  motion,  also  supplies  the  requisite  degree  of  steadiness. 
When  the  tail  is  lashed  from  side  to  side  there  is  a  tendency 
to  produce  a  corresponding  movement  in  the  head,  which 
is  at  once  corrected  by  the  complementary  curve.  $or  is 
this  all ;  the  cephalic  curve,  in  conjunction  with  the  water 
contained  within  it,  forms  the  point  d'appui  for  the  caudal 
curve,  and  vice  versa.  When  a  fish  swims,  the  anterior  and 
posterior  portions  of  its  body  (supposing  it  to  be  a  short- 
bodied  fish)  form  curves,  the  convexities  of  which  are 
directed  on  opposite  sides  of  a  given  line,  as  is  the  case 
in  the  extremities  of  the  biped  when  walking.  The  mass 
of  the  fish,  like  the  mass  of  the  biped,  when  once  set  in 
motion,  contributes  to  progression  by  augmenting  the  rate 
of  speed.  The  velocity  acquired  by  certain  fishes  is  very 
great.  A  shark  can  gambol  around  the  bows  of  a  ship  in 
full  sail ;  and  a  sword-fish  (such  is  the  momentum  acquired 
by  it)  has  been  known  to  thrust  its  tusk  through  the  copper 
sheathing  of  a  vessel,  a  layer  of  felt,  four  inches  of  deal,  and 
fourteen  inches  of  oaken  plank.1 

The  wing  of  the  bird  does  not  materially  differ  from  the 
•  A  portion  of  the  timbers,  etc.,  of  one  of  Her  Majesty's  ships,  having  tho 


1 2  ANIMAL  LOCOMOTION. 

extremity  of  the  biped  or  the  tail  of  the  fish.  It  is  con- 
structed on  a  similar  plan,  and  acts  on  the  same  principle. 
The  tail  of  the  fish,  the  wing  of  the  bird,  and  the  extremity 
of  the  biped  and  quadruped,  are  screws  structurally  and 
functionally.  In  proof  of  this,  compare  the  bones  of  the  wing 
of  a  bird  with  the  bones  of  the  arm  of  a  man,  or  those  of  the 
fore-leg  of  an  elephant,  or  any  other  quadruped.  In  either 
case  the  bones  are  twisted  upon  themselves  like  the  screw  of 
an  augur.  The  tail  of  the  fish,  the  extremities  of  the  biped  and 
quadruped,  and  the  wing  of  the  bird,  when  moving,  describe 
waved  tracks.  Thus  the  wing  of  the  bird,  when  it  is  made 
to  oscillate,  is  thrown  into  double  or  figure-of-8  curves,  like 
the  body  of  the  fish.  When,  moreover,  the  wing  ascends  and 
descends  to  make  the  up  and  down  strokes,  it  rotates  within 
the  facettes  or  depressions  situated  on  the  scapula  and  coracoid 
bones,  precisely  in  the  same  way  that  the  arm  of  a  man  rotates 
in  the  glenoid  cavity,  or  the  leg  in  the  acetabular  cavity  in 
the  act  of  walking.  The  ascent  and  descent  of  the  wing  in 
flying  correspond  to  the  steps  made  by  the  extremities  in 
walking ;  the  wing  rotating  upon  the  body  of  the  bird  during 
the  down  stroke,  the  body  of  the  bird  rotating  on  the  wing 
during  the  up  stroke.  When  the  wing  descends  it  describes 
a  downward  and  forward  curve,  and  elevates  the  body  in  an 
upward  and  forward  curve.  When  the  body  descends,  it 
describes  a  downward  and  forward  curve,  the  wing  being 
elevated  in  an  upward  and  forward  curve.  The  curves 
made  by  the  wing  and  body  in  flight  form,  when  united, 
waved  lines,  which  intersect  each  other  at  every  beat  of 
the  wing.  The  wing  and  the  body  act  upon  each  other 
alternately  (the  one  being  active  when  the  other  is  passive), 
and  the  descent  of  the  wing  is  not  more  necessary  to  the 
elevation  of  the  body  than  the  descent  of  the  body  is  to 
the  elevation  of  the  wing.  It  is  thus  that  the  weight  of  the 
flying  animal  is  utilized,  slip  avoided,  and  continuity  of  move- 
ment secured. 

As  to  the  actual  waste  of  tissue  involved  in  walking,  swim- 
ming, and  flying,  there  is  much  discrepancy  of  opinion.    It  is 

tusk  of  a  sword-fish  imbedded  in  it,  is  to  be  seen  in  the  Hunteri.au  Museum 
of  the  Royal  College  of  Surgeons  of  England. 


INTRODUCTION.  1 3 

commonly  believed  that  a  bird  exerts  quite  an  enormous 
amount  of  power  as  compared  with  a  fish  ;  a  fish  exerting  a 
much  greater  power  than  a  land  animal.  This,  there  can  be 
no  doubt,  is  a  popular  delusion.  A  bird  can  fly  for  a  whole 
day,  a  fish  can  swim  for  a  whole  day,  and  a  man  can  walk 
for  a  whole  day.  If  so,  the  bird  requires  no  greater  power 
than  the  fish,  and  the  fish  than  the  man.  The  speed  of  the 
bird  as  compared  with  that  of  the  fish,  or  the  speed  of  the 
fish  as  compared  with  that  of  the  man,  is  no  criterion  of  the 
power  exerted.  The  speed  is  only  partly  traceable  to  the 
power.  As  has  just  been  stated,  it  is  due  in  a  principal 
measure  to  the  shape  and  size  of  the  travelling  surfaces,  the 
density  of  the  medium  traversed,  the  resistance  experienced 
to  forward  motion,  and  the  part  performed  by  the  mass 
of  the  animal,  when  moving  and  acting  upon  its  travel- 
ling surfaces.  It  is  erroneous  to  suppose  that  a  bird  is 
stronger,  weight  for  weight,  than  a  fish,  or  a  fish  than  a 
man.  It  is  equally  erroneous  to  assume  that  the  exer- 
tions of  a  flying  animal  are  herculean  as  compared  with 
those  of  a  walking  or  swimming  animal.  Observation  and 
experiment  incline  me  to  believe  just  the  opposite.  A  flying 
creature,  when  fairly  launched  in  space  (because  of  the  part 
which  weight  plays  in  flight,  and  the  little  resistance  expe- 
rienced in  forward  motion),  sweeps  through  the  air  with 
almost  no  exertion.1  This  is  proved  by  the  sailing  flight  of 
the  albatross,  and  by  the  fact  that  some  insects  can  fly  when 
two-thirds  of  their  wing  area  have  been  removed.  (This  ex- 
periment is  detailed  further  on.)  These  observations  are 
calculated  to  show  the  grave  necessity  for  studying  the  media 
to  be  traversed ;  the  fulcra  which  the  media  furnish,  and  the 
size,  shape,  and  movements  of  the  travelling  surfaces.  The 
travelling  surfaces  of  animals,  as  has  been  already  explained, 
furnish  the  levers  by  whose  instrumentality  the  movements 
of  walking,  swimming,  and  flying  are  effected. 

1  A  flying  creature  exerts  its  greatest  power  wlien  rising.  The  effort  is  of 
short  duration,  and  inaugurates  rather  than  perpetuates  flight.  If  the  volant 
animal  can  launch  into  space  from  a  height,  the  preliminary  effort  may  be 
dispensed  with  as  in  this  case,  the  weight  of  the  animal  acting  upon  the 
Inclined  planes  formed  by  the  wings  gets  up  the  initial  velocity. 


1 4  ANIMAL  LOCOMOTION. 

By  comparing  the  flipper  of  the  seal,  sea-bear,  and  walrus 
with  the  fin  and  tail  of  the  fish,  whale,  porpoise,  etc.;  and 
the  wing  of  the  penguin  (a  bird  which  is  incapable  of  flight, 
and  can  only  swim  and  dive)  with  the  wing  of  the  insect, 
bat,  and  bird,  I  have  been  able  to  show  that  a  close  analogy 
exists  between  the  flippers,  fins,  and  tails  of  sea  mammals 
and  fishes  on  the  one  hand,  and  the  wings  of  insects,  bats, 
and  birds  on  the  other ;  in  fact,  that  theoretically  and  prac- 
tically these  organs,  one  and  all,  form  flexible  helices  or 
screws,  which,  in  virtue  of  their  rapid  reciprocating  move- 
ments, operate  upon  the  water  and  air  by  a  wedge-action  after 
the  manner  of  twisted  or  double  inclined  planes.  The  twisted 
inclined  planes  act  upon  the  air  and  water  by  means  of 
curved  surfaces,  the  curved  surfaces  reversing,  reciprocating, 
and  engendering  a  wave  pressure,  which  can  be  continued 
indefinitely  at  the  will  of  the  animal.  The  wave  pressure 
emanates  in  the  one  instance  mainly  from  the  tail  of  the  fish, 
whale,  porpoise,  etc.,  and  in  the  other  from  the  wing  of  the 
insect,  bat,  or  bird — the  reciprocating  and  opposite  curves  into 
which  the  tail  and  wing  are  thrown  in  swimming  and  flying 
constituting  the  mobile  helices,  or  screivs,  which,  during  their 
action,  produce  the  precise  kind  and  degree  of  pressure 
adapted  to  fluid  media,  and  to  which  they  respond  with  the 
greatest  readiness. 

In  order  to  prove  that  sea  mammals  and  fishes  swim,  and 
insects,  bats,  and  birds  fly,  by  the  aid  of  curved  figure- of-8 
surfaces,  which  exert  an  intermittent  wave  pressure,  I  con- 
structed artificial  fish-tails,  fins,  flippers,  and  wings,  which 
curve  and  taper  in  every  direction,  and  which  are  flexible 
and  elastic,  particularly  towards  the  tips  and  posterior  mar- 
gins. These  artificial  fish-tails,  fins,  flippers,  and  wings  are 
slightly  twisted  upon  themselves,  and  when  applied  to  the 
water  and  air  by  a  sculling  or  figure-of-8  motion,  curiously 
enough  reproduce  the  curved  surfaces  and  movements  peculiar 
to  real  fish-tails,  fins,  flippers,  and  wings,  in  swimming,  and 
flying. 

Propellers  formed  on  the  fish-tail  and  wing  model  are,  I 
find,  the  most  effective  that  can  be  devised,  whether  for 
navigating  the  water  or  the  air.  To  operate  efficiently  on 


INTRODUCTION.  15 

fluid,  i.e.  yielding  media,  the  propeller  itself  must  yield.  Of 
this  I  am  fully  satisfied  from  observation  and  experiment. 
The  propellers  at  present  employed  in  navigation  are,  in  my 
opinion,  faulty  both  in  principle  and  application. 

The  observations  and  experiments  recorded  in  the  present 
volume  date  from  1864.  In  1867  I  lectured  on  the  subject  of 
animal  mechanics  at  the  Royal  Institution  of  Great  Britain  : l 
in  June  of  the  same  year  (1867)  I  read  a  memoir  "  On  the 
Mechanism  of  Flight"  to  the  Linnean  Society  of  London  ;2 
and  in  August  of  1870  I  communicated  a  memoir  "  On  the 
Physiology  of  Wings"  to  the  Royal  Society  of  Edinburgh.3 
These  memoirs  extend  to  200  pages  quarto,  and  are  illus- 
trated by  190  original  drawings.  The  conclusions  at  which 
I  arrived,  after  a  careful  study  of  the  movements  of  walking, 
swimming,  and  flying,  are  briefly  set  forth  in  a  letter  addressed 
to  the  French  Academy  of  Sciences  in  March  1870.  This 
the  Academy  did  me  the  honour  of  publishing  in  April  of 
that  year  (1870)  in  the  Comptes  Rendus,  p.  875.  In  it  I 
claim  to  have  been  the  first  to  describe  and  illustrate  the 
following  points,  viz.  : — 

That  quadrupeds  walk,  and  fishes  swim,  and  insects,  bats, 
and  birds  fly  by  figure-of-8  movements. 

That  the  flipper  of  the  sea  bear,  the  swimming  wing  of  the 
penguin,  and  the  wing  of  the  insect,  bat,  and  bird,  are  screws 
structurally,  and  resemble  the  blade  of  an  ordinary  screw- 
propeller. 

That  those  organs  are  screws  functionally,  from  their  twist- 
ing and  untwisting,  and  from  their  rotating  in  the  direction 
of  their  length,  when  they  are  made  to  oscillate. 

That  they  have  a  reciprocating  action,  and  reverse  their 
planes  more  or  less  completely  at  every  stroke. 

That  the  wing  describes  a  figure-of-8  track  in  space  when 
the  flying  animal  is  artificially  fixed. 

That  the  wing,  when  the  flying  animal  is  progressing  at 

1  "  On  the  various  modes  of  Flight  in  relation  to  Aeronautics." — Proceed- 
ings of  the  Royal  Institution  of  Great  Britain,  March  22,  1867. 

•  "  On  the  Mechanical  Appliances  by  which  Flight  is  attained  in  the 
Animal  Kingdom."— Transactions  of  the  Linnean  Society,  vol.  xxvi. 

3  "  On  the  Phymology  of  Wings." — Transactions  of  the  lloyal  Society  of 
Edinburgh,  vol.  xxvi. 


16  ANIMAL  LOCOMOTION. 

a  high  speed  in  a  horizontal  direction,  describes  a  looped 
and  then  a  waved  track,  from  the  fact  that  the  figure  of 
8  is  gradually  opened  out  or  unravelled  as  the  animal 
advances. 

That  the  wing  acts  after  the  manner  of  a  kite,  both  during 
the  down  and  up  strokes. 

I  was  induced  to  address  the  above  to  the  French  Academy 
from  finding  that,  nearly  two  years  after  I  had  published  my 
views  on  the  figure  of  8,  looped  and  wave  movements  made 
by  the  wing,  etc.,  Professor  E.  J.  Marey  (College  of  France, 
Paris)  published  a  course  of  lectures,  in  which  the  peculiar 
figure-of-8  movements,  first  described  and  figured  by  me, 
were  put  forth  as  a  new  discovery.  The  accuracy  of  this 
statement  will  be  abundantly  evident  when  I  mention 
that  my  first  lecture,  "  On  the  various  modes  of  Flight  in 
relation  to  Aeronautics,"  was  published  in  the  Proceedings 
of  the  Royal  Institution  of  Great  Britain  on  the  22d  of 
March  1867,  and  translated  into  French  (Revue  des  cours 
scientifiques  de  la  France  et  de  1'Etranger)  on  the  21st  of 
September  1867;  whereas  Professor  Marey's  first  lecture, 
"  On  the  Movements  of  the  Wing  in  the  Insect "  (Revue  des 
cours  scientifiques  de  la  France  et  de  1'Etranger),  did  not 
appear  until  the  13th  of  February  1869. 

Professor  Marey,  in  a  letter  addressed  to  the  French 
Academy  in  reply  to  mine,  admits  my  claim  to  priority  in 
the  following  terms  : — 

"  J'ai  constat6  qu'effectivement  M.  Pettigrew  a  vu  avant 
moi,  et  represent^  dans  son  Memoire,  la  forme  en  8  du  par- 
cours  de  1'aile  de  1'insecte  :  que  la  methode  optique  &  laquelle 
j'avais  recours  est  a  peu  pres  identique  a  la  sienne.  .  .  .  Je 
m'empresse  de  satisfaire  a  cette  demande  legitime,  et  de  laisser 
entierement  la  priorit6  sur  moi  a  M.  Pettigrew  relativement 
a  la  question  ainsi  restreirite." — (Comptes  Rendus,  May  16, 
1870,  p.  1093). 

The  figure-of-8  theory  of  walking,  swimming,  and  flying, 
as  originally  propounded  in  the  lectures,  papers,  and  memoirs 
referred  to,  has  been  confirmed  not  only  by  the  researches 
and  experiments  of  Professor  Marey,  but  also  by  those  of  M. 
Senecal,  M.  de  Fastes,  M.  Ciotti,  and  others.  Its  accuracy  is 


INTRODUCTION.  1 7 

no  longer  a  matter  of  doubt.  As  the  limits  of  the  present 
volume  will  not  admit  of  my  going  into  the  several  arrange- 
ments by  which  locomotion  is  attained  in  the  animal  king- 
dom as  a  whole,  I  will  only  describe  those  movements  which 
illustrate  in  a  progressive  manner  the  several  kinds  of  pro- 
gression on  the  land,  and  on  and  in  the  water  and  air. 

I  propose  first  to  analyse  the  natural  movements  of  walk- 
ing, swimming,  and  flying,  after  which  I  hope  to  be  able  to 
show  that  certain  of  these  movements  may  be  reproduced 
artificially.  The  locomotion  of  animals  depends  upon  me- 
chanical adaptations  found  in  all  animals  which  change  local- 
ity. These  adaptations  are  very  various,  but  under  whatever 
guise  they  appear  they  are  substantially  those  to  which  we 
resort  when  we  wish  to  move  bodies  artificially.  Thus  in 
animal  mechanics  we  have  to  consider  the  various  orders  of 
levers,  the  pulley,  the  centre  of  gravity,  specific  gravity,  the 
resistance  of  solids,  semi-solids,  fluids,  etc.  As  tHe  laws  which 
regulate  the  locomotion  of  animals  are  essentially  those  which 
regulate  the  motion  of  bodies  in  general,  it  will  be  necessary 
to  consider  briefly  at  this  stage  the  properties  of  matter  when 
at  rest  and  when  moving.  They  are  well  stated  by  Mr. 
Bishop  in  a  series  of  propositions  which  I  take  the  liberty  of 
transcribing : — 

"  Fundamental  Axioms. — First,  every  body  continues  in  a 
state  of  rest,  or  of  uniform  motion  in  a  right  line,  until  a 
change  is  effected  by  the  agency  of  some  mechanical  force. 
Secondly,  any  change  effected  in  the  quiescence  or  motion  of 
a  body  is  in  the  direction  of  the  force  impressed,  and  is  pro- 
portional to  it  in  quantity.  Thirdly,  reaction  is  always  equal 
and  contrary  to  action,  or  the  mutual  actions  of  two  bodies 
upon  each  other  are  always  equal  and  in  opposite  directions. 

Of  uniform  motion. — If  a  body  moves  constantly  in  the 
same  manner,  or  if  it  passes  over  equal  spaces  in  equal  periods 
of  time,  its  motion  is  uniform.  The  velocity  of  a  body  moving 
uniformly  is  measured  by  the  space  through  which  it  passes 
in  a  given  time. 

The  velocities  generated  or  impressed  on  different  masses 
by  the  same  force  are  reciprocally  as  the  masses. 

Motion  uniformly  varied. — When  the  motion  of  a  body  is 


18  ANIMAL  LOCOMOTION. 

uniformly  accelerated,  the  space  it  passes  through  during  any 
time  whatever  is  proportional  to  the  square  of  the  time. 

In  the  leaping,  jumping,  or  springing  of  animals  in  any 
direction  (except  the  vertical),  the  paths  they  describe  in 
their  transit  from  one  point  to  another  in  the  plane  of  motion 
are  parabolic  curves. 

The  legs  move  by  the  force  of  gravity  as  a  pendulum. — The 
Professor,  Weber,  have  ascertained,  that  when  the  legs  of 
animals  swing  forward  in  progressive  motion,  they  obey  the 
same  laws  as  those  which  regulate  the  periodic  oscillations  of 
the  pendulum. 

Resistance  of  fluids. — Animals  moving  in  air  and  water 
experience  in  those  media  a  sensible  resistance,  which  is 
greater  or  less  in  proportion  to  the  density  and  tenacity  of 
the  fluid,  and  the  figure,  superficies,  and  velocity  of  the  animal. 

An  inquiry  into  the  amount  and  nature  of  the  resistance 
of  air  and  water  to  the  progression  of  animals  will  also  furnish 
the  data  for  estimating  the  proportional  values  of  those  fluids 
acting  as  fulcra  to  their  locomotive  organs,  whether  they  be 
fins,  wings,  or  other  forms  of  lever. 

The  motions  of  air  and  water,  and  their  directions,  exer- 
cise very  important  influences  over  velocity  resulting  from 
muscular  action. 

Mechanical  effects  of  fluids  on  animals  immersed  in  them. — 
When  a  body  is  immersed  in  any  fluid  whatever,  it  will  lose 
as  much  of  its  weight  relatively  as  is  equal  to  the  weight  of 
the  fluid  it  displaces.  In  order  to  ascertain  whether  an 
animal  will  sink  or  swim,  or  be  sustained  without  the  aid  of 
muscular  force,  or  to  estimate  the  amount  of  force  required 
that  the  animal  may  either  sink  or  float  in  water,  or  fly  in 
the  air,  it  will  be  necessary  to  have  recourse  to  the  specific 
gravities  both  of  the  animal  and  of  the  fluid  in  which  it  is 
placed. 

The  specific  gravities  or  comparative  weights  of  different 
substances  are  the  respective  weights  of  equal  volumes  of 
those  substances. 

Centre  of  gravity. — The  centre  of  gravity  of  any  body  is 
a  point  about  which,  if  acted  upon  only  by  the  force  of 
gravity,  it  will  balance  itself  in  all  positions ;  or,  it  is  a  point 


INTIIODUCTION.  19 

which,  if  supported,  the  body  will  be  supported,  however  it 
may  be  situated  in  other  respects ;  and  hence  the  effects  pro- 
duced by  or  upon  any  body  are  the  same  as  if  its  whole  mass 
were  collected  into  its  centre  of  gravity. 

The  attitudes  and  motions  of  every  animal  are  regulated 
by  the  positions  of  their  centres  of  gravity,  which,  in  a  state 
of  rest,  and  not  acted  upon  by  extraneous  forces,  must  lie  in 
vertical  lines  which  pass  through  their  basis  of  support. 

In  most  animals  moving  on  solids,  the  centre  is  supported 
by  variously  adapted  organs ;  during  the  flight  of  birds  and 
insects  it  is  suspended ;  but  in  fishes,  which  move  in  a  fluid 
whose  density  is  nearly  equal  to  their  specific  gravity,  the 
centre  is  acted  upon  equally  in  all  directions."  l 

As  the  locomotion  of  the  higher  animals,  to  which  my 
remarks  more  particularly  apply,  is  in  all  cases  effected  by 
levers  which  differ  in  no  respect  from  those  employed  in  the 
arts,  it  may  be  useful  to  allude  to  them,  in  a  passing  wa}r. 
This  done,  I  will  consider  the  bones  and  joints  of  the  skeleton 
which  form  the  levers,  and  the  muscles  which  move  them. 

"  The  Lever. — Levers  are  commonly  divided  into  three  kinds, 
according  to  the  relative  positions  of  the  prop  or  fulcrum,  the 
power,  and  the  resistance  or  weight.  The  straight  lever  of 
each  order  is  equally  balanced  when  the  power  multiplied  by 
its  distance  from  the  fulcrum  equals  the  weight,  multiplied  by 
its  distance,  or  P  the  power,  and  W  the  weight,  are  in  equi- 
librium when  they  are  to  each  other  in  the  inverse  ratio  of 
the  arms  of  the  lever,  to  which  they  are  attached.  The 
pressure  on  the  fulcrum  however  varies. 

A.  F          B 


In  straight  levers  of  the  first  kind,  the  fulcrum  is  between 
the  power  and  the  resistance,  as  in  fig.  1,  where  F  is 
the  fulcrum  of  the  lever  AB ;  P  is  the  power,  and  "VV  the 
weight  or  resistance.  We  have  P  :  W  :  :  BF  :  AF,  hence 

1  Cyc.  of  Anat.  and  Phy.,  Art.  "Motion,"  by  John  Bishop,  Esq. 


20  ANIMAL  LOCOMOTION. 

P.AF=:W.BF,  and  the  pressure  on  the  fulcrum  is  both  the 
power  and  resistance,  or  P+W. 

In  the  second  order  of  levers  (fig.  2),  the  resistance  is  be- 
tween the  fulcrum  and  the  power ;  and,  as  before,  P  :  W  : : 
BF  :  AF,  but  the  pressure  of  the  fulcrum  is  equal  to  W— P, 
or  the  weight  less  the  power. 


B 


FIG.  2. 

In  the  third  order  of  lever  the  power  acts  between  the  prop 
and  the  resistance  (fig.  3),  where  also  P  :  W  :  :  BF  :  AF,  and  the 
pressure  on  the  fulcrum  is  P— W,  or  the  power  less  the  weight. 


Fio.  3. 

In  the  preceding  computations  the  weight  of  the  lever 
itself  is  neglected  for  the  sake  of  simplicity,  but  it  obviously 
forms  a  part  of  the  elements  under  consideration,  especially 
with  reference  to  the  arms  and  legs  of  animals. 

To  include  the  weight  of  the  lever  we  have  the  following 
equations  :  P.  AF^AF.fAF  =  W.  BF  +  BF.  J  BF ;  in  the 
first  order,  where  AF  and  BF  represent  the  weights  of  these 
portions  of-  the  lever  respectively.  Similarly,  in  the  second 

AF 
order   P.  AF  =  W.BF  +  AF.  — - -,   and  in  the  third   order 

BF 


INTRODUCTION. 


21 


In  this  outline  of  the  theory  of  the  lever,  the  forces  have 
been  considered  as  acting  vertically,  or  parallel  to  the  direc- 
tion of  the  force  of  gravity. 

Passive  Organs  of  Locomotion.  Bones. — The  solid  frame- 
work or  skeleton  of  animals  which  supports  and  protects  their 
more  delicate  tissues,  whether  chemically  composed  of  ento- 
moline,  carbonate,  or  phosphate  of  lime ;  whether  placed  in- 
ternally or  externally ;  or  whatever  may  be  its  form  or 
dimensions,  presents  levers  and  fulcra  for  the  action  of  the 
muscular  system,  in  all  animals  furnished  with  earthy  solids 
for  their  support,  and  possessing  locomotive  power."1  The 
levers  and  fulcra  are  well  seen  in  the  extremities  of  the  deer, 
the  skeleton  of  which  is  selected  for  its  extreme  elegance. 


Fin.  4.  Skeleton  of  the  Deer  (after  Pander  and  D'Alton).  The  bones  in  the  ex- 
tremities of  this  the  fleetest  of  quadrupeds  are  inclined  very  obliquely  towards 
each  other,  and  towards  the  scapular  and  iliac  bones.  This  arrangement  in- 
creases the  leverage  of  the  muscular  system  and  confers  great  rapidity  on 
the  moving  parts.  It  augments  elasticity,  diminishes  shock,  and  indirectly 
begets  continuity  of  movement,  a.  Angle  formed  by  the  femur  with  the 
ilium.  &.  Angle  formed  by  the  tibia  and  fibula  with  the  femur,  c.  Angle 
formed  by  the  cannon  bone  with  the  tibia  and  fibula,  d.  Angle  formed  by 
the  phalanges  with  the  cannon  bone.  e.  Angle  formed  by  the  humerus  with 
the  scapula.  /.  Angle  formed  by  the  radius  and  ulna  with  the  humerus. 

1  Bishop,  op.  cit. 


22  ANIMAL  LOCOMOTION. 

While  the  bones  of  animals  form  levers  and  fulcra  for  portions 
of  the  muscular  system,  it  must  never  be  forgotten  that  the 
earth,  water,  or  air  form  fulcra  for  the  travelling  surfaces  of 
animals  as  a  whole.  Two  sets  of  fulcra  are  therefore  always 
to  be  considered,  viz.  those  represented  by  the  bones,  and 
those  represented  by  the  earth,  water,  or  air  respectively. 
The  former  when  acted  upon  by  the  muscles  produce  motion 
in  different  parts  of  the  animal  (not  necessarily  progressive 
motion)  ;  the  latter  when  similarly  influenced  produce  loco- 
motion. Locomotion  is  greatly  favoured  by  the  tendency 
which  the  body  once  set  in  motion  has  to  advance  in  a  straight 
line.  The  form,  strength,  density,  and  elasticity  of  the  skele- 
ton varies  in  relation  to  the  bulk  and  locomotive  power  of 
the  animal,  and  to  the  media  in  which  it  is  destined  to  move. 

"  The  number  of  moveable  articulations  in  a  skeleton  de- 
termines the  degree  of  its  mobility  within  itself;  and  the 
kind  and  number  of  the  articulations  of  the  locomotive  organs 
determine  the  number  and  disposition  of  the  muscles  acting 
upon  them. 

The  bones  of  vertebrated  animals,  especially  those  which 
are  entirely  terrestrial,  are  much  more  elastic,  hard,  and 
calculated  by  their  chemical  elements  to  bear  the  shocks  and 
strains  incident  to  terrestrial  progression,  than  those  of  the 
aquatic  vertebrata  ;  the  bones  of  the  latter  being  more  fibrous 
and  spongy  in  their  texture,  the  skeleton  is  more  soft  and 
yielding. 

The  bones  of  the  higher  orders  of  animals  are  constructed 
according  to  the  most  approved  mechanical  principles.  Thus 
they  are  convex  externally,  concave  within,  and  strengthened 
by  ridges  running  across  their  discs,  as  in  the  scapular  and 
iliac  bones ;  an  arrangement  which  affords  large  surfaces  for 
the  attachment  of  the  powerful  muscles  of  locomotion.  The 
bones  of  birds  in  many  cases  are  not  filled  with  marrow  but 
with  air, — a  circumstance  which  insures  that  they  shall  be 
very  strong  and  very  light. 

In  the  thigh  bones  of  most  animals  an  angle  is  formed  by 
the  head  and  neck  of  the  bone  with  the  axis  of  the  body, 
which  prevents  the  weight  of  the  superstructure  coming 
vertically  upon  the  shaft,  converts  the  bone  into  an  elastic 


INTRODUCTION.  23 

arch,  and  renders  it  capable  of  supporting  the  weight  of  the 
body  in  standing,  leaping,  and  in  falling  from  considerable 
altitudes. 

Joints. — Where  the  limbs  are  designed  to  move  to  and 
fro  simply  in  one  plane,  the  ginglymoid  or  hinge-joint  is  ap- 
plied ;  and  where  more  extensive  motions  of  the  limbs  are 
requisite,  the  enarthrodial,  or  ball-and-socket  joint,  is  intro- 
duced. These  two  kinds  of  joints  predominate  in  the  locomo- 
tive organs  of  the  animal  kingdom. 

The  enarthrodial  joint  has  by  far  the  most  extensive  power 
of  motion,  and  is  therefore  selected  for  uniting  the  limbs  to  the 
trunk.  It  permits  of  the  several  motions  of  the  limbs  termed 
pronation,  supination,  flexion,  extension,  abduction,  adduc- 
tion, and  revolution  upon  the  axis  of  the  limb  or  bone  about  a 
conical  area,  whose  apex  is  the  axis  of  the  head  of  the  bone, 
and  base  circumscribed  by  the  distal  extremity  of  the  limb." l 

The  ginglymoid  or  hinge-joints  are  for  the  most  part  spiral  in 
their  nature.  They  admit  in  certain  cases  of  a  limited  degree  of 
lateral  rocking.  Much  attention  has  been  paid  to  the  subject 
of  joints  (particularly  human  ones)  by  the  brothers  Weber, 
Professor  Meyer  of  Zurich,  and  likewise  by  Langer,  Henke, 
Meissuer,  and  Goodsir.  Langer,  Henke,  and  Meissner  suc- 
ceeded in  demonstrating  the  "  screw  configuration"  of  the 
articular  surfaces  of  the  elbow,  ankle,  and  calcaneo-astraga- 
loid  joints,  and  Goodsir  showed  that  the  articular  surface 
of  the  knee-joint  consist  of  "  a  double  conical  screw  combina- 
tion." The  last-named  observer  also  expressed  his  belief 
"  that  articular  combinations  with  opposite  windings  on 
opposite  sides  of  the  body,  similar  to  those  in  the  knee-joint, 
exist  in  the  ankle  and  tarsal,  and  in  the  elbow  and  carpal 
joints  ;  and  that  the  hip  and  shoulder  joints  consist  of  single 
threaded  couples,  but  also  with  opposite  windings  on  oppo- 
site sides  of  the  body."  I  have  succeeded  in  demonstrating 
a  similar  spiral  configuration  in  the  several  bones  and  joints 
of  the  wing  of  the  bat  and  bird,  and  in  the  extremities  of 
most  quadrupeds.  The  bones  of  animals,  particularly  the 
extremities,  are,  as  a  rule,  twisted  levers,  and  act  after  the 
manner  of  screws.  This  arrangement  enables  the  higher 
1  Bishop,  op.  cit. 


24  ANIMAL  LOCOMOTION. 

animals  to  apply  their  travelling  surfaces  to  the  media  on 
which  they  are  destined  to  pperate  at  any  degree  of  obliquity 
so  as  to  obtain  a  maximum  of  support  or  propulsion  with  a 
minimum  of  slip.  If  the  travelling  surfaces  of  animals  did 
not  form  screws  structurally  aud  functionally,  they  could 
neither  seize  nor  let  go  the  fulcra  on  which  they  act  with  the 
requisite  rapidity  to  secure  speed,  particularly  in  water  and  air. 

"Ligaments. — The  office  of  the  ligaments  with  respect  to 
locomotion,  is  to  restrict  the  degree  of  flexion,  extension,  and 
other  motions  of  the  limbs  within  definite  limits. 

Effect  of  Atmospheric  pressure  on  Limbs. — The  influence  of 
atmospheric  pressure  in  supporting  the  limbs  was  first  noticed 
by  Dr.  Arnott,  though  it  has  been  erroneously  ascribed  by 
Professor  Miiller  to  Weber.  Subsequent  experiments  made 
by  Dr.  Todd,  Mr.  Wormald,  and  others,  have  fully  established 
the  mechanical  influence  of  the  air  in  keeping  the  mechanism 
of  the  joints  together.  The  amount  of  atmospheric  pressure 
on  any  joint  depends  upon  the  area  or  surface  presented  to 
its  influence,  and  the  height  of  the  barometer.  According  to 
Weber,  the  atmospheric  pressure  on  the  hip-joint  of  a  man 
is  about  26  Ibs.  The  pressure  on  the  knee-joint  is  estimated 
by  Dr.  Arnott  at  60  Ibs."1 

Active  organs  of  Locomotion.  Muscles,  their  Properties,  Ar- 
rangement, Mode  of  Action,  etc. — If  time  and  space  had  per- 
mitted, I  would  have  considered  it  my  duty  to  describe,  more 
or  less  fully,  the  muscular  arrangements  of  all  the  animals 
whose  movements  I  propose  to  analyse.  This  is  the  more 
desirable,  as  the  movements  exhibited  by  animals  of  the 
higher  types  are  directly  referable  to  changes  occurring  in 
their  muscular  system.  As,  however,  I  could  not  hope  to 
overtake  this  task  within  the  limits  prescribed  for  the  present 
work,  I  shall  content  myself  by  merely  stating  the  properties 
of  muscles ;  the  manner  in  which  muscles  act ;  and  the  man- 
ner in  which  they  are  grouped,  with  a  view  to  moving  the 
osseous  levers  which  constitute  the  bony  framework  or  skele- 
ton of  the  animals  to  be  considered.  Hitherto,  and  by 
common  consent,  it  has  been  believed  that  whereas  a  flexor 
muscle  is  situated  on  one  aspect  of  a  limb,  and  its  correspond- 
1  Bishop,  op.  cit. 


INTRODUCTION.  25 

ing  extensor  on  the  other  aspect,  these  two  muscles  must  be 
opposed  to  and  antagonize  each  other.  This  belief  is  founded 
on  what  I  regard  as  an  erroneous  assumption,  viz.,  that  muscles 
have  only  the  power  of  shortening,  and  that  when  one 
muscle,  say  the  flexor,  shortens,  it  must  drag  out  and  forcibly 
elongate  the  corresponding  extensor,  and  the  converse.  This 
would  be  a  mere  waste  of  power.  Nature  never  works 
against  herself.  There  are  good  grounds  for  believing,  as  I 
have  stated  elsewhere,1  that  there  is  no  such  thing  as  antagon- 


Fio.  5.  Shows  the  muscular  cycle  formed  by  the  biceps  (a)  or  flexor  muscle, 
and  the  triceps  (h)  or  extensor  muscle  of  the  human  arm.  At  i  the  centri- 
petal or  shortening  action  of  the  biceps  is  seen,  and  atj  the  centrifugal  or 
elongating  action  of  the  triceps  (vide  arrows).  The  present  figure  represents 
the  forearm  as  flexed  upon  the  arm.  As  a  consequence,  the  long  axes  of  the 
sareous  elements  or  ultimate  particles  of  the  biceps  (i)  are  arranged  in  a 
more  or  less  horizontal  direction;  the  long  axes  of  the  sareous  elements  of 
the  triceps  (j)  being  arranged  in  ii  nearly  vertical  direction.  When  the  fore- 
arm is  extended,  the  long  axes  of  the  sareous  elements  of  the  biceps  and 
triceps  are  reversed.  The  present  figure  shows  how  the  bones  of  the  ex- 
tremities form  levers,  and  how  they  are  moved  by  muscular  action  If, 
e.g.,  the  biceps  (a)  shortens  and  the  triceps  (6)  elongates,  they  cause  the  fore- 
arm and  hand  (h)  to  move  to  wards  the  shoulder  (d).  If,  on  the  other  hand,  the 
triceps  (6)  shortens  and  the  biceps  (a)  elongates,  they  cause  the  forearm  and 
hand  (h)  to  move  away  from  the  shoulder.  In  these  actions  the  biceps  (a)  and 
triceps  (&)  are  the  power;  the  elbow-joint  (g]  the  fulcrum,  and  the  foreann 
and  hand  (h)  the  weight  to  be  elevated  or  depressed.  If  the  hand  repre- 
sented a  travelling  surface  which  operated  on  the  earth,  the  water,  or  the 
air,  it  is  not  difficult  to  understand  how,  when  it  was  made  to  move  by 
the  action  of  the  muscles  of  the  arm,  it  would  in  turn  move  the  body  to 
which  it  belonged,  d  Coracoid  process  of  the  scapula,  from  which  the  internal 
or  short  head  of  the  biceps  (a)  arises,  e  Insertion  of  the  biceps  into  the 
radius.  /  Long  head  of  the  triceps  (6).  g  Insertion  of  the  triceps  into  the 
olecranon  process  of  the  ulna. — Oriqinal. 

ism  in  muscular  movements ;  the  several  muscles  known  as 
flexors  and  extensors;  abductors  and  adductors;  pronators 
and  supinators,  being  simply  correlated.  Muscles,  when  they 

1  "  Lectures  on  the  Physiology  of  the  Circulation  in  Plants,  in  the  Lower 
Animals,  and  in  Man."— Edinburgh  Medical  Journal  for  January  and  Feb- 
ruary 1873. 


26  ANIMAL  LOCOMOTION. 

act,  operate  upon  bones  or  something  extraneous  to  them- 
selves, and  not  upon  each  other.  The  muscles  are  folded 
round'  the  extremities  and  trunks  of  animals  with  a  view  to 
operating  in  masses.  For  this  purpose  they  are  arranged  in 
cycles,  there  being  what  are  equivalent  to  extensor  and  flexor 
cycles,  abductor  and  adductor  cycles,  and  pronator  and  supina- 
tor  cycles.  Within  these  muscular  cycles  the  bones,  or 
extraneous  substances  to  be  moved,  are  placed,  and  when  one 
side  of  a  cycle  shortens,  the  other  side  elongates.  Muscles 
are  therefore  endowed  with  a  centripetal  and  centrifugal 
action.  These  cycles  are  placed  at  every  degree  of  obliquity 
and  even  at  right  angles  to  each  other,  but  they  are  so  dis- 
posed in  the  bodies  and  limbs  of  animals  that  they  always 
operate  consentaneously  and  in  harmony.  Fide  fig.  5,  p.  25. 
There  are  in  animals  very  few  simple  movements,  i.e. 
movements  occurring  in  one  plane  and  produced  by  the  action 
of  two  muscles.  Locomotion  is  for  the  most  part  produced 
by  the  consentaneous  action  of  a  great  number  of  muscles ; 
these  or  their  fibres  pursuing  a  variety  of  directions.  This  is 
particularly  true  of  the  movements  of  the  extremities  in  walk- 
ing, swimming,  and  flying. 

Muscles  are  divided  into  the  voluntary,  the  involuntary,  and 
the  mixed,  according  as  the  will  of  the  animal  can  wholly, 
partly,  or  in  no  way  control  their  movements.  The  voluntary 
muscles  are  principally  concerned  in  the  locomotion  of  animals. 
They  are  the  power  which  moves  the  several  orders  of  levers 
into  which  the  skeleton  of  an  animal  resolves  itself. 

The  movements  of  the  voluntary  and  involuntary  muscles 
are  essentially  wave-like  in  character,  i.e.  they  spread  from 
certain  centres,  according  to  a  fixed  order,  and  in  given  direc- 
tions. In  the  extremities  of  animals  the  centripetal  or  con- 
verging muscular  wave  on  one  side  of  the  bone  to  be  moved, 
is  accompanied  by  a  corresponding  centrifugal  or  diverging 
wave  on  the  other  side ;  the  bone  or  bones  by  this  arrangement 
being  perfectly  under  control  and  moved  to  a  hair's-breadth. 
The  centripetal  or  converging,  and  the  centrifugal  or  diverging 
waves  of  force  are,  as  already  indicated,  correlated.1  Similar 
remarks  may  be  made  regarding  the  different  parts  of  the  body 
1  Muscles  virtually  possess  a  pulling  and  pushing  power;  the  pushing 


INTRODUCTION.  27 

of  the  serpent  when  creeping,  of  the  body  of  the  fish  when 
swimming,  of  the  wing  of  the  bird  when  flying,  and  of  our  own 
extremities  when  walking.  In  all  those  cases  the  moving 
parts  are  thrown  into  curves  or  waves  definitely  correlated. 

It  may  be  broadly  stated,  that  in  every  case  locomotion  is 
the  result  of  the  opening  and  closing  of  opposite  sides  of 
muscular  cycles.  By  the  closing  or  shortening,  say  of  the 
flexor  halves  of  the  cycles,  and  the  opening  or  elongation  of 
the  extensor  halves,  the  angles  formed  by  the  osseous  levers 
are  diminished ;  by  the  closing  or  shortening  of  the  extensor 
halves  of  the  cycles,  and  the  opening  or  elongation  of  the 
flexor  halves,  the  angles  formed  by  the  osseous  levers  are 
increased.  This  alternate  diminution  and  increase  of  the 
angles  formed  by  the  osseous  levers  produce  the  movements 
of  walking,  swimming,  and  flying.  The  muscular  cycles  of 
the  trunk  and  extremities  are  so  disposed  with  regard  to  the 
bones  or  osseous  levers,  that  they  in  every  case  produce  a 
maximum  result  with  a  minimum  of  power.  The  origins 
and  insertions  of  the  muscles,  the  direction  of  the  muscles  and 
the  distribution  of  the  muscular  fibres  insure,  that  if  power 
is  lost  in  moving  a  lever,  speed  is  gained,  there  being  an 
apparent  but  never  a  real  loss.  The  variety  and  extent  of 
movement  is  secured  by  the  obliquity  of  the  muscular  fibres 
to  their  tendons ;  by  the  obliquity  of  the  tendons  to  the  bones 
they  are  to  move ;  and  by  the  proximity  of  the  attachment 
of  the  muscles  to  the  several  joints.  As  muscles  are  capable 
of  shortening  and  elongating  nearly  a  fourth  of  their  length, 
they  readily  produce  the  precise  kind  and  degree  of  motion 
required  in  any  particular  case.1 

The  force  of  muscles,  according  to  the  experiments  of 
Schwann,  increases  with  their  length,  and  vice  versa.  It  is  a 
curious  circumstance,  and  worthy  the  attention  of  those  in- 
terested in  homologies,  that  the  voluntary  muscles  of  the 

power  being  feeble  and  obscured  by  the  flaccidity  of  the  muscular  mass.  In 
order  to  push  effectually,  tlie  pushing  substance  must  be  more  or  less  rigid. 

1  The  extensor  muscles  preponderate  in  mass  and  weight  over  the  flexors, 
but  this  is  readily  accounted  for  by  the  fact,  that  the  extensors,  when  limbs 
are  to  be  straightened,  always  work  at  a  mechanical  disadvantage.  This  is 
owing  to  the  shape  of  the  bones,  the  conformation  of  the  joints,  and  the 
position  occupied  by  the  extensors. 


28 


ANIMAL  LOCOMOTION. 


superior  and  inferior  extremities,  and  more  especially  of  the4 
trunk,  are  arranged  in  longitudinal,  transverse,  and  oblique 
spiral  lines,  and  in  layers  or  strata  precisely  as  in  the 
ventricles  of  the  heart  and  hollow  muscles  generally.1  If, 
consequently,  I  eliminate  the  element  of  bone  from  these 
several  regions,  I  reproduce  a  typical  hollow  muscle;  and 
what  is  still  more  remarkable,  if  I  compare  the  bones  re- 
moved (say  the  bones  of  the  anterior  extremity  of  a  quad- 
ruped or  bird)  with  the  cast  obtained  from  the  cavity  of  a 
hollow  muscle  (say  the  left  ventricle  of  the  heart  of  the 
mammal),  I  find  that  the  bones  and  the  cast  are  twisted 
upon  themselves,  and  form  elegant  screws,  the  threads  or 
ridges  of  which  run  in  the  same  direction.  This  affords  a 
proof  that  the  involuntary  hollow  muscles  supply  the  type  or 


Fio.  ((.—Wing  of  bird.  Shows  how  the  bones  of  the  arm  (a),  forearm  (ft),  and 
hand  (c),  are  twisted,  and  form  a  conical  screw.  Compare  with  Figs.  7 
and  8.— Original 


Fio.  7. 


Fio.  7.— Anterior  extremity  of  elephant.    Shows  how  the  bones  of  the  arm  (7), 
jrearni  (q'x),  and  foot  (o).  are  twisted  to  form  an  osseous  screw.    Compare 


with  Figs.  6  and  8.— Original. 
Fio.  8.— Castor  mould  of  the  interior  of  the  left  ventricle  of  the  heart  of  a 
Shows  that  the  left  ventricular  cavity  is  conical  and  spiral  in  its 
lire,    a  Portion  of  right  ventricular  cavity  ;  b,  base  of  left  ventricular 
cavity  ;  x,  y,  spiral  grooves  occupied  by  the  spiral  musculi  papillares  ;  jq, 
spiral  ridges  projecting  between  the  musculi  papillares.   Compare  with  Figs. 
6  and  7.  —Original. 

pattern  on  which  the  voluntary  muscles  are  formed.  Fig.  6  re- 
presents the  bones  of  the  wing  of  the  bird;  fig.  7  the  bones  of  the 
"  On  the  Arrangement  of  the  Muscular  Fibres  in  the  Ventricles  of  the 
Vertebrate  Heart,  with  Physiological  Remarks,"  by  the  Author.— Philo- 
sophical Transactions,  1864. 


INTRODUCTION.  29 

anterior  extremity  of  the  elephant ;  and  fig.  8  the  cast  or  mould 
of  the  cavity  of  the  left  ventricle  of  the  heart  of  the  deer. 

It  has  been  the  almost  invariable  custom  in  teaching 
anatomy,  arid  such  parts  of  physiology  as  pertain  to  animal 
movements,  to  place  much  emphasis  upon  the  configuration 
of  the  bony  skeleton  as  a  whole,  and  the  conformation  of  its 
several  articular  surfaces  in  particular.  This  is  very  natural, 
as  the  osseous  system  stands  the  wear  and  tear  of  time,  while 
all  around  it  is  in  a  great  measure  perishable.  It  is  the  link 
which  binds  extinct  forms  to  living  ones,  and  we  naturally 
venerate  and  love  what  is  enduring.  It  is  no  marvel  that 
Oken,  Goethe,  Owen,  and  others  should  have  attempted  such 
splendid  generalizations  with  regard  to  the  osseous  system — 
should  have  proved  with  such  cogency  of  argument  that  the 
head  is  an  expanded  vertebra.  The  bony  skeleton  is  a  miracle 
of  design  very  wonderful  and  very  beautiful  in  its  way.  But 
when  all  has  been  said,  the  fact  remains  that  the  skeleton, 
when  it  exists,  forms  only  an  adjunct  of  locomotion  and 
motion  generally.  All  the  really  essential  movements  of  an 
animal  occur  in  its  soft  parts.  The  osseous  system  is  there- 
fore to  be  regarded  as  secondary  in  importance  to  the  mus- 
cular, of  which  it  may  be  considered  a  differentiation.  Instead 
of  regarding  the  muscles  as  adapted  to  the  bones,  the  bones 
ought  to  be  regarded  as  adapted  to  the  muscles.  Bones  have 
no  power  either  of  originating  or  perpetuating  motion.  This 
begins  and  terminates  in  the  muscles.  Nor  must  it  be  over- 
looked, that  bone  makes  its  appearance  comparatively  late  in 
the  scale  of  being ;  that  innumerable  creatures  exist  in  which 
no  trace  either  of  an  external  or  internal  skeleton  is  to  be 
found ;  that  these  creatures  move  freely  about,  digest,  circu- 
late their  nutritious  juices  and  blood  when  present,  multiply, 
and  perform  all  the  functions  incident  to  life.  While  the 
skeleton  is  to  be  found  in  only  a  certain  proportion  of  the 
animals  existing  on  our  globe,  the  soft  parts  are  to  be  met 

"  On  the  Muscular  Arrangements  of  the  Bladder  and  Prostate,  and  the 
manner  in  which  the  Ureters  and  Urethra  are  closed,"  by  the  Author. — 
Philosophical  Transactions,  18G7. 

"  On  the  Muscular  Tunics  in  the  Stomach  of  Man  and  other  Mammalia," 
1>y  the  Author.— Proceedings  Royal  Society  of  London,  1867. 


30 


ANIMAL  LOCOMOTION. 


with  in  all ;  and  this  appears  to  me  an  all-sufficient  reason 
for  attaching  great  importance  to  the  movements  of  soft 
parts,  such  as  protoplasm,  jelly  masses,  involuntary  and  volun- 
tary muscles,  etc.1  As  the  muscles  of  vertebrates  are  accu- 
rately applied  to  each  other,  and  to  the  bones,  while  the  bones 
are  rigid,  unyielding,  and  incapable  of  motion,  it  follows  that 
the  osseous  system  acts  as  a  break  or  boundary  to  the  muscular 
one, — and  hence  the  arbitrary  division  of  muscles  into  exten- 
sors and  flexors,  pronators  and  supinators,  abductors  and  ad- 
ductors. This  division  although  convenient  is  calculated  to 
mislead.  The  most  highly  organized  animal  is  strictly  speaking 
to  be  regarded  as  a  living  mass  whose  parts  (hard,  soft,  and 


Fio  9.— The  Superficial  Muscles  in  the  Horse,  (after  Bagg). 

otherwise)  are  accurately  adapted  to  each  other,  every  part 
reciprocating  with  scrupulous  exactitude,  and  rendering  it 
tfficult  to  determine  where  motion  begins  and  where  it  ter- 
minates.    Fig.  9  shows  the  more  superficial  of  the  muscular 
«  which  move  the  bones  or  osseous  levers  of  the  horse, 
as  seen  m  the  walk,  trot,  gallop,  etc.     A  careful  examination 
;e  carneous  masses  or  muscles  will  show  that  they  run 
_>  Lectures  «  On  the  Physiology  of  the  Circulation  in  Plants,  in  the  Lower 
'"         "  ^  *'  AUtl'°r' "  E<1inhursh  Me<1ical  Journal  for  SeP" 


INTRODUCTION.  31 

longitudinally,  transversely,  and  obliquely,  the  longitudinal 
and  transverse  muscles  crossing  each  other  at  nearly  right 
angles,  the  oblique  ones  tending  to  cross  at  various  angles,  as 
in  the  letter  X.  The  crossing  is  seen  to  most  advantage  in 
the  deep  muscles. 

In  order  to  understand  the  twisting  which  occurs  to  a 
greater  or  less  extent  in  the  bodies  and  extremities  (when 
present)  of  all  vertebrated  animals,  it  is  necessary  to  reduce  the 
bony  and  muscular  systems  to  their  simplest  expression.  If 
motion  is  desired  in  a  dorsal,  ventral,  or  lateral  direction  only,  a 
dorsal  and  ventral  or  a  right  and  left  lateral  set  of  longitudinal 
muscles  acting  upon  straight  bones  articulated  by  an  ordinary 
ball-and-socket  joint  will  suffice.  In  this  case  the  dorsal, 
ventral,  and  right  and  left  lateral  muscles  form  miiscular  cycles  ; 
contraction  or  shortening  on  the  one  aspect  of  the  cycle  being 
accompanied  by  relaxation  or  elongation  on  the  other,  the 
bones  and  joints  forming  as  it  were  the  diameters  of  the 
cycles,  and  oscillating  in  a  backward,  forward,  or  lateral 
direction  in  proportion  to  the  degree  and  direction  of  the 
muscular  movements.  Here  the  motion  is  confined  to  two 
planes  intersecting  each  other  at  right  angles.  When,  how- 
ever, the  muscular  system  becomes  more  Wghly  differentiated, 
both  as  regards  the  number  of  the  muscles  employed,  and  the 
variety  of  the  directions  pursued  by  them,  the  bones  and 
joints  also  become  more  complicated.  Under  these  circum- 
stances, the  bones,  as  a  rule,  are  twisted  upon  themselves, 
and  their  articular  surfaces  present  various  degrees  of  spirality 
to  meet  the  requirements  of  the  muscular  system.  Between  the 
straight  longitudinal  muscles,  therefore,  arranged  in  dorsal  and 
ventral,  and  right  and  left  lateral  sets,  and  those  which  run  in  a 
more  or  less  transverse  direction,  and  between  the  simple  joint 
whose  motion  is  confined  to  one  plane  and  the  ball-and-socket 
joints  whose  movements  are  universal,  every  degree  of  obli- 
quity is  found  in  the  direction  of  the  muscles,  and  every  pos- 
sible modification  in  the  disposition  of  the  articular  surfaces. 
In  the  fish  the  muscles  are  for  the  most  part  arranged  in 
dorsal,  ventral,  and  lateral  sets,  which  run  longitudinally;  and, 
as  a  result,  the  movements  of  the  trunk,  particularly  towards 
the  tail,  are  from  side  to  side  and  sinuous.  As,  however, 


32  ANIMAL  LOCOMOTION. 

oblique  fibres  are  also  present,  and  the  tendons  of  the  longi- 
tudinal muscles  in  some  instances  cross  obliquely  towards  the 
tail,  the  fish  has  also  the  power  of  tilting  or  twisting  its 
trunk  (particularly  the  lower  half)  as  well  as  the  caudal  fin. 
In  a  mackerel  which  I  examined,  the  oblique  muscles  were 
represented  by  the  four  lateral  masses  occurring  between  the 
dorsal,  ventral,  and  lateral  longitudinal  muscles — two  of 
these  being  found  on  either  side  of  the  fish,  and  corresponding 
to  the  myocommas  or  "  grand  muscle  lateral"  of  Cuvier.  The 
muscular  system  of  the  fish  would  therefore  seem  to  be  ar- 
ranged on  a  fourfold  plan, — there  being  four  sets  of  longi- 
tudinal muscles,  and  a  corresponding  number  of  slightly 
oblique  and  oblique  muscles,  the  oblique  muscles  being  spiral 
in  their  nature  and  tending  to  cross  or  intersect  at  various 
angles,  an  arrest  of  the  intersection,  as  it  appears  to  me, 
giving  rise  to  the  myocommas  and  to  that  concentric  arrange- 
ment of  their  constituent  parts  so  evident  on  transverse 
section.  This  tendency  of  the  muscular  fibres  to  cross 
each  other  at  various  degrees  of  obliquity  may  also  be  traced 
in  several  parts  of  the  human  body,  as,  for  instance,  in  the 
deltoid  muscle  of  the  arm  and  the  deep  muscles  of  the  leg. 
Numerous  other  examples  of  penniform  muscles  might  be 
adduced.  Although  the  fibres  of  the  myocommas  have  a 
more  or  less  longitudinal  direction,  the  myocommas  them- 
selves pursue  an  oblique  spiral  course  from  before  backwards 
and  from  within  outwards,  i.e.  from  the  spine  towards  the 
periphery,  where  they  receive  slightly  oblique  fibres  from  the 
longitudinal  dorsal,  ventral,  and  lateral  muscles.  As  the 
spiral  oblique  myocommas  and  the  oblique  fibres  from  the 
longitudinal  muscles  act  directly  and  indirectly  upon  the 
spines  of  the  vertebrae,  and  the  vertebrae  themselves  to  which 
they  are  specially  adapted,  and  as  both  sets  of  oblique  fibres 
are  geared  by  interdigitation  to  the  fourfold  set  of  longitu- 
dinal muscles,  the  lateral,  sinuous,  and  rotatory  movements  of 
the  body  and  tail  of  the  fish  are  readily  accounted  for. 
The  spinal  column  of  the  fish  facilitates  the  lateral  sinuous 
twisting  movements  of  the  tail  and  trunk,  from  the  fact  that 
the  vertebrae  composing  it  are  united  to  each  other  by  a  series 
of  modified  universal  joints— the  vertebne  supplying  the  cup- 


INTRODUCTION.  33 

shaped  depressions  or  sockets,  the  intervertebral  substance, 
the  prominence  or  ball. 

The  same  may  be  said  of  the  general  arrangement  of  the 
muscles  in  the  trunk  and  tail  of  the  Cetacea,  the  principal 
muscles  in  this  case  being  distributed,  not  on  the  sides,  but 
on  the  dorsal  and  ventral  aspects.  The  lashing  of  the  tail 
in  the  whales  is  consequently  from  above  downwards  or 
vertically,  instead  of  from  side  to  side.  The  spinal  column  is 
jointed  as  in  the  fish,  with  this  difference,  that  the  vertebrae 
(especially  towards  the  tail)  form  the  rounded  prominences  or 
ball,  the  meniscus  or  cup-shaped  intervertebral  plates  the 
receptacles  or  socket. 

When  limbs  are  present,  the  spine  may  be  regarded  as 
being  ideally  divided,  the  spiral  movements,  under  these 
circumstances,  being  thrown  upon  the  extremities  by  typical 
ball-and-socket  joints  occurring  at  the  shoulders  and  pelvis. 
This  is  peculiarly  the  case  in  the  seal,  where  the  spirally 
sinuous  movements  of  the  spine  are  transferred  directly  to 
the  posterior  extremities.1 

The  extremities,  when  present,  are  provided  with  their 
own  muscular  cycles  of  extensor  and  flexor,  abductor  and 
adductor,  pronator  and  supinator  muscles, — these  running 
longitudinally  and  at  various  degrees  of  obliquity,  and  en- 
veloping the  hard  parts  according  to  their  direction — the 
bones  being  twisted  upon  themselves  and  furnished  with 
articular  surfaces  which  reflect  the  movements  of  the 
muscular  cycles,  whether  these  occur  in  straight  lines  an- 
teriorly, posteriorly,  or  laterally,  or  in  oblique  lines  in  inter- 
mediate situations.  The  straight  and  oblique  muscles  are 
principally  brought  into  play  in  the  movements  of  the  extremi- 

1  That  the  movements  of  the  extremities  primarily  emanate  from  the  spine  is 
rendered  probable  by  the  remarkable  powers  possessed  by  serpents.  "  It  is 
true,"  writes  Professor  Owen  (op.  tit.  p.  261),  "  that  the  serpent  has  no  limbs, 
yet  it  can  outclimb  the  monkey,  outswim  the  fish,  outleap  the  jerboa,  and, 
suddenly  loosing  the  close  coils  of  its  crouching  spiral,  it  can  spring  into  the 
air  and  seize  the  bird  upon  the  wing."  ....  "The  serpent  has  neither 
hands  nor  talons,  yet  it  can  outwrestle  the  athlete,  and  crush  the  tiger  in  the 
embrace  of  its  ponderous  overlapping  folds."  The  peculiar  endowments, 
which  accompany  the  possession  of  extremities,  it  appears  to  me,  present 
themselves  in  an  undeveloped  or  latent  form  in  the  trunk  of  the  reptile. 


34  ANIMAL  LOCOMOTION. 

ties  of  quadrupeds,  bipeds,  etc.  in  walking;  in  the  move- 
ments of  the  tails  and  fins  of  fishes,  whales,  etc.  in  swimming ; 
and  in  the  movements  of  the  wings  of  insects,  bats,  and 
birds  in  flying.  The  straight  and  oblique  muscles  are 
usually  found  together,  and  co-operate  in  producing  the 
movements  in  question ;  the  amount  of  rotation  in  a  part 
always  increasing  as  the  oblique  muscles  preponderate.  The 
combination  of  ball-and-socket  and  hinge-joints,  with  their  con- 
comitant oblique  and  longitudinal  muscular  cycles  (the  former 
occurring  in  their  most  perfect  forms  where  the  extremities 
are  united  to  the  trunk,  the  latter  in  the  extremities  them- 
selves), enable  the  animal  to  present,  when  necessary,  an  exten- 
sive resisting  surface  the  one  instant,  and  a  greatly  diminished 
and  a  comparatively  non-resisting  one  the  next.  This  arrange- 
ment secures  the  subtlety  and  nicety  of  motion  demanded  by 
the  several  media  at  different  stages  of  progression. 

The  travelling  surfaces  of  Animals  modified  and  adapted 
to  the  medium  on  or  in  which  they  move. — In  those  land 
animals  which  take  to  the  water  occasionally,  the  feet,  as  a 


FIG.  10.         Fio.  11.  FIG.  12.  Fio.  13.  Fio.  14. 

FIG.  10.— Extreme   form   of  compressed  foot,  as  seen  m  the  deer,  ox,  etc., 

adapted  specially  for  land  transit.— Original. 
Fio    11.— Extreme    form  of  expanded  foot,  as  seen  in  the  Ornithorhynchits, 

etc.,  adapted  more  particularly  for  swimming.—  Original 
Fios.  12  and  13.— Intermediate  form  of  foot,  as  seen  hi  the  otter  (tig    12), 

frog  (fig.   13),  etc.     Here  the  foot  is  equally  serviceable  in  and  out  of  the 

water.—  Original. 


Original 


rule,  are  furnished  with  membranous  expansions  extend- 
ing between  the  toes.  Of  such  the  Otter  (fig.  12),  Ornitho- 
rhynchus  (fig.  n)r  Seal  (fig  14)?  Crocodile5  Sea-Bear  (fig.  37, 
P;  76),  ANalnis,  Frog  (fig.  13),  and  Triton,  may  be  cited. 
Ahe  crocodile  and  triten,  in  addition  to  the  membranous 


INTRODUCTION. 


35 


expansion  occurring  between  the  toes,  are  supplied  with  a 
powerful  swimming-tail,  which  adds  very  materially  to  the 
surface  engaged  in  natation.  Those  animals,  one  and  all, 
walk  awkwardly,  it  always  happening  that  when  the  ex- 
tremities are  modified  to  operate  upon  two  essentially 
different  media  (as,  for  instance,  the  land  and  water),  the 
maximum  of  speed  is  attained  in  neither.  For  this  reason 
those  animals  which  swim  the  best,  walk,  as  a  rule,  with  the 
greatest  difficulty,  and  vice  versd,  as  the  movements  of  the 
auk  and  seal  in  and  out  of  the  water  amply  testify. 

In  addition  to  those  land  animals  which  run  and  swim, 
there  are  some  which  precipitate  themselves,  parachute- 
fashion,  from  immense  heights,  and  others  which  even  fly. 
In  these  the  membranous  expansions  are  greatly  increased, 
the  ribs  affording  the  necessary  support  in  the  Dragon  or 
Flying  Lizard  (fig.  15),  the  anterior  and  posterior  extremities 
and  tail,  in  the  Flying  Lemur  (fig.  16)  and  Bat  (fig.  17,  p.  36). 


Fio.  15. 


Pio.  16. 


Fro.  15.— The  Red-throated  Dragon  (Drncn  hrpmatopngon,  Gray)  shows  a  large 
membranous  expansion  (ft  fc)  situated  between  the  anterior  (</</)  and  pos- 
terior extremities,  and  supported  by  the  ribs.  The  dragon  by  this  arrange- 
ment can  take  extensive  leaps  with  perfect  safety. — Original. 

Fin.  16.— The  Flying  Lemur  iCatespitlifi-H*  rtilniis,  Shaw).  In  the  flying 
lemur  the  membranous  expansion  (a  ft)  is  more  extensive  than  in  the 
Flying  Dragon  (fig.  ];V.  It  is  supported  by  the  neck,  back,  and  tail,  and 
by  the  anterior  and  posterior  extremities.  The  flying  lemur  takes  enor- 
mous leaps;  its  membranous  tunic  all  but  enabling  it  to  fly.  The  Rat, 
Pln/llnrhina  firiirilis  (fig.  17),  flics  with  a  very  slight  increase  of  surface. 
The  surface  exposed  by  the  bat  exceeds  that  displayed  by  many  insects 


36  ANIMAL  LOCOMOTION. 

and  birds.  The  wings  of  the  bat  are  deeply  concave,  and  so  resemble  the 
wings  of  beetles  and  heavy-bodied  short-winged  birds.  The  bones  of  the 
arm  (r),  forearm  (</),  and  hand  (n,  n,  n)  of  the  bat  (fig.  17)  support  the 
anterior  or  thick  7iiargin  and  the  extremity  of  the  wing,  and  may  not  inaptly 
be  compared  to  the  nervures  in  corresponding  positions  in  the  wing  of 
the  beetle. — Original. 


Fia.  17. — The  Bat  (Phyllorhina  gracilis,  Peters).  Here  the  travelling-surfaces 
(rdef,  aim  n)  are  enormously  increased  as  compared  with  that  of  the 
land  and  water  animals  generally.  Compare  with  figures  from  10  to  14, 
p.  34.  r  Arm  of  bat ;  d  forearm  of  bat ;  ef,nnn  hand  of  bat.  —Original. 

Although  no  lizard  is  at  present  known  to  fly,  there  can 
be  little  doubt  that  the  extinct  Pterodactyles  (which,  accord- 
ing to  Professor  Huxley,  are  intermediate  between  the  lizards 
and  crocodiles)  were  possessed  of  this  power.  The  bat  is 
interesting  as  being  the  only  mammal  at  present  endowed 
with  wings  sufficiently  large  to  enable  it  to  fly.1  It  affords 
an  extreme  example  of  modification  for  a  special  purpose, — 
its  attenuated  body,  dwarfed  posterior,  and  greatly  elongated 
anterior  extremities,  with  their  enormous  fingers  and  out- 
spreading membranes,  completely  unfitting  it  for  terrestrial 
progression.  It  is  instructive  as  showing  that  flight  may  be 
attained,  without  the  aid  of  hollow  bones  and  air-sacs,  by 
purely  muscular  efforts,  and  by  the  mere  diminution  and 
increase  of  a  continuous  membrane. 

As  the  flying  lizard,  flying  lemur,  and  bat  (figs.  15,  16,  and 
17,  pp.  35  and  36),  connect  terrestrial  progression  with  aerial 
progression,  so  the  auk,  penguin  (fig.  46,  p.  91),  and  flying- 
fish  (fig.  51,  p.  98),  connect  progression  in  the  water  with 
progression  in  the  air.  The  travelling  surfaces  of  these  ano- 
malous creatures  run  the  movements  peculiar  to  the  three 
highways  of  nature  into  each  other,  and  bridge  over,  as  it 
were,  the  gaps  which  naturally  exist  between  locomotion  on 
the  land,  in  the  water,  and  in  the  air. 

1  The  Vampire  Bat  of  the  Island  of  Bonin,  according  to  Dr.  Buckland,  can 
also  swim  ;  and  this  authority  was  of  opinion  that  the  Pterodactyle  enjoyed 
similar  ad  vantages. —Eng.  Cycl.  vol.  iv.  p.  495. 


PROGRESSION  ON  THE  LAND. 


Walking  of  the  Quadruped,  Biped,  etc. — As  the  earth,  because 
of  its  solidity,  will  bear  any  amount  of  pressure  to  which  it 
may  be  subjected,  the  size,  shape,  and  weight  of  animals 
destined  to  traverse  its  surface  are  matters  of  little  or  no 
consequence.  As,  moreover,  the  surface  trod  upon  is  rigid 
or  unyielding,  the  extremities  of  quadrupeds  are,  as  a  rule, 
terminated  by  small  feet.  Fig.  1 8  (contrast  with  fig.  1 7). 


Fio.  18.— Cliillingham  Bull  (Tins  Scotints).  Shows  powerful  heavy  body,  and 
the  small  extremities  adapted  for  land  transit.  Also  the  figure-of-8  move- 
ments made  liy  the  feet  and  limbs  in  walking  and  running,  w,  t  Curves 
made  by  right  and  left  anterior  extremities,  r,  s  Curves  made  by  right 
and  left  posterior  extremities.  The  right  fore  and  the  left  hind  foot  move 
together  to  form  the  waved  line  (s,  «) ;  the  left  fore  and  the  right  hind  foot 
move  together  to  form  the  waved  line  (r,  t).  The  curves  formed  by  the 
anterior  (t.  »/.)  and  posterior  (r,  s)  extremities  form  ellipses.  Compare  with 
fig.  19,  p.  39.— Original. 

In  this  there  is  a  double  purpose — the  limited  area  pre- 
sented to  the  ground  affording  the  animal  sufficient  support 
and  leverage,  and  enabling  it  to  disentangle  its  feet  with  the 


38  ANIMAL  LOCOMOTION. 

utmost  facility,  it  being.a  condition  in  rapid  terrestrial  pro- 
gression that  the  points  presented  to  the  earth  be  few  in 
number  and  limited  in  extent,  as  this  approximates  the  feet 
of  animals  most  closely  to  the  wheel  in  mechanics,  where  the 
surface  in  contact  with  the  plane  of  progression  is  reduced  to 
a  minimum.  When  the  surface  presented  to  a  dense  resisting 
medium  is  increased,  speed  is  diminished,  as  shown  in  the 
tardy  movements  of  the  mollusc,  caterpillar,  and  slowworm, 
and  also,  though  not  to  the  same  extent,  in  the  serpents, 
some  of  which  move  with  considerable  celerity.  In  the  gecko 
and  common  house-fly,  as  is  well  known,  the  travelling  sur- 
faces are  furnished  with  suctorial  discs,  which  enable  those 
creatures  to  walk,  if  need  be,  in  an  inverted  position ;  and 
"  the  tree-frogs  (Hyla)  have  a  concave  disc  at  the  end  of  each 
toe,  for  climbing  and  adhering  to  the  bark  and  leaves  of  trees. 
Some  toads,  on  the  other  hand,  are  enabled,  by  peculiar 
tubercles  or  projections  from  the  palm  or  sole,  to  clamber  up 
old  walls."1  A  similar,  but  more  complicated  arrangement, 
is  met  with  in  the  arms  of  the  cuttle-fish. 

The  movements  of  the  extremities  in  land  animals  vary 
considerably. 

In  the  kangaroo  and  jerboa,2  the  posterior  extremities 
only  are  used,  the  animals  advancing  per  saltum,  i.e.  by  a 
series  of  leaps.3 

The  deer  also  bounds  into  the  air  in  its  slower  movements; 
in  its  fastest  paces  it  gallops  like  the  horse,  as  explained  at 
pp.  40-44.  The  posterior  extremities  of  the  kangaroo  are 
enormously  developed  as  compared  with  the  anterior  ones ; 
they  are  also  greatly  elongated.  The  posterior  extremities 
are  in  excess,  likewise,  in  the  horse,  rabbit,4  agouti,  and  guinea 

1  Comp.  Anat.  and  Phys.  of  Vertebrates,  by  Professor  Owen,  vol.  i.  pp. 
262,  263.  Lond.  1866. 

*  The  jerboa  when  pursued  can  leap  a  distance  of  nine  feet,  and  repeat  the 
leaps  so  rapidly  that  it  cannot  be  overtaken  even  by  the  aid  of  a  swift  horse. 
The  bullfrog,  a  much  smaller  animal,  can,  when  pressed,  clear  from  six  to 
eight  feet  at  each  bound,  and  project  itself  over  a  fence  five  feet  high. 

3  The  long,  powerful  Uil  of  the  kangaroo  assists  in  maintaining  the  equi- 
librium of  the  animal  prior  to  the  leaps;   the  posterior  extremities  and 
tail  forming  a  tripod  of  support. 

4  The  rabbit  occasionally  takes  several  short  steps  with  the  fore  legs  and 


PROGRESSION  ON  THE  LAND.  39 

pig.  As  a  consequence  these  animals  descend  declivities  with 
difficulty.  They  are  best  adapted  for  slightly  ascending  ground. 
In  the  giraffe  the  anterior  extremities  are  longer  and  more 
powerful,  comparatively,  than  the  posterior  ones,  which  is 
just  the  opposite  condition  to  that  found  in  the  kangaroo. 

In  the  giraffe  the  legs  of  opposite  sides  move  together  and 
alternate,  whereas  in  most  quadrupeds  the  extremities  move 
diagonally — a  remark  which  holds  true  also  of  ourselves  in 
walking  and  skating,  the  right  leg  and  left  arm  advancing 
together  and  alternating  with  the  left  leg  and  right  arm  (fig.  1 9). 


FIG.  19. — Diagram  showing  the  .figure-of-S  or  double-waved  track  produced  by 
the  alternating  of  the  extremities  in  man  in  walking  and  running ;  the 
right  leg  (r)  and  left  arm  (s)  advancing  simultaneously  to  form  one  step  ; 
and  alternating  with  tho  left,  leg  (t)  and  right  arm  (u),  which  likewise  ad- 
vance together  to  form  a  second  step.  The  continuous  line  (r,  t)  gives  the 
waved  track  made  by  the  legs  ;  the  interrupted  line  (s,  u)  that  made  by  the 
arms.  The  curves  made  by  the  right  leg  and  left  arm,  and  by  the  left  leg 
and  right  arm,  form  ellipses.  Compare  with  fig.  18,  p.  37.— Original. 

In  the  hexapod  insects,  according  to  Miiller,  the  fore  and 
hind  foot  of  the  one  side  and  the  middle  one  of  the  opposite 
side  move  together  to  make  one  step,  the  three  corresponding 
and  opposite  feet  moving  together  to  form  the  second  step. 
Other  and  similar  combinations  are  met  with  in  the  decapods. 

The  alternating  movements  of  the  extremities  are  interest- 
ing as  betokening  a  certain  degree  of  flexuosity  or  twisting, 
either  in  the  trunk  or  limbs,  or  partly  in  the  one  and  partly 
in  the  other. 

This  twisting  begets  the  figure-of-8  movements  observed  in 
walking,  swimming,  and  flying.  (Compare  figs.  6,  7,  and  26  x, 
pp.  28  and  55  ;  figs.  18  and  19,  pp.  37  and  39  ;  figs.  32  and  50, 
pp.  68  and  97  ;  figs.  71  and  73,  p.  144  ;  and  fig.  81,  p.  157.) 

Locomotion  of  the  Horse. — As  the  limits  of  the  present 
volume  forbid  my  entering  upon  a  consideration  of  the  move- 
ments of  all  the  animals  with  terrestrial  habits,  I  will  describe 
briefly,  and  by  way  of  illustration,  those  of  the  horse,  ostrich, 

one  long  one  with  the  hind  legs  ;  so  that  it  walks  with  the  fore  legs,  and  leaps 
with  the  hind  ones. 


40  ANIMAL  LOCOMOTION. 

and  man.  In  the  horse,  as  in  all  quadrupeds  endowed  with 
great  speed,  the  bones  of  the  extremities  are  inclined  obliquely 
towards  each  other  to  form  angles ;  the  angles  diminishing  as 
the  speed  increases.  Thus  the  angles  formed  by  the  bones  of 
the  extremities  with  each  other  and  with  the  scapulae  and 
iliac  bones,  are  less  in  the  horse  than  in  the  elephant.  For 
the  same  reason  they  are  less  in  the  deer  than  in  the  horse. 
In  the  elephant,  where  no  great  speed  is  required,  the  limbs 
are  nearly  straight,  this  being  the  best  arrangement  for  sup- 
porting superincumbent  weight.  The  angles  formed  by  the 
different  bones  of  the  wing  of  the  bird  are  less  than  in  the 
fleetest  quadruped,  the  movements  of  wings  being  more  rapid 
than  those  of  the  extremities  of  quadrupeds  and  bipeds. 
These  are  so  many  mechanical  adaptations  to  neutralize  shock, 
to  increase  elasticity,  and  secure  velocity.  The  paces  of  the 
horse  are  conveniently  divided  into  the  walk,  the  trot,  the 
amble,  and  the  gallop.  If  the  horse  begins  his  walk  by  rais- 
ing his  near  fore  foot,  the  order  in  which  the  feet  are  lifted  is 
as  follows  : — first  the  left  fore  foot,  then  the  right  or  diagonal 
hind  foot,  then  the  right  fore  foot,  and  lastly  the  left  or 
diagonal  hind  foot.  There  is  therefore  a  twisting  of  the 
body  and  spiral  overlapping  of  the  extremities  of  the  horse 
in  the  act  of  walking,  in  all  respects  analogous  to  what 
occurs  in  other  quadrupeds l  and  in  bipeds  (figs.  1 8  and  1 9,  pp. 
37  and  39).  In  the  slowest  walk  Mr.  Gamgee  observes  "  that 
three  feet  are  in  constant  action  on  the  ground,  whereas  in 
the  free  walk  in  which  the  hind  foot  passes  the  position  from 
which  the  parallel  fore  foot  moves,  there  is  a  fraction  of  time 
when  only  two  feet  are  upon  the  ground,  but  the  interval  is 
too  short  for  the  eye  to  measure  it.  The  proportion  of  time, 
therefore,  during  which  the  feet  act  upon  the  ground,  to  that 
occupied  in  their  removal  to  new  positions,  is  as  three  to  one 
in  the  slow,  and  a  fraction  less  in  the  fast  walk.  In  the  fast 
gallop  these  proportions  are  as  five  to  three.  In  all  the  paces 
the  power  of  the  horse  is  being  exerted  mainly  upon  a  fore 

If  a  cat  when  walking  is  seen  from  above,  a  continuous  wave  of  move- 
ment is 'observed  travelling  along  its  spine  from  before  backwards.  This 
movement  closely  resembles  the  crawling  of  the  serpent  and  the  swimming  of 
the  eel. 


PROGRESSION  ON  THE  LAND.  41 

and  hind  limb,  with  the  feet  implanted  in  diagonal  positions. 
There  is  also  a  constant  parallel  line  of  positions  kept  up  by 
a  fore  and  hind  foot,  alternating  sides  in  each  successive  move. 
These  relative  positions  are  renewed  and  maintained.  Thus 
each  fore  limb  assumes,  as  it  alights,  the  advanced  position 
parallel  with  the  hind,  just  released  and  moving ;  the  hind 
feet  move  by  turns,  in  sequence  to  their  diagonal  fore,  and  in 
priority  to  their  parallel  fellows,  which  following  they  main- 
tain for  nearly  half  their  course,  when  the  fore  in  its  turn  is 
raised  and  carried  to  its  destined  place,  the  hind  alighting 
midway.  All  the  feet  passing  over  equal  distances  and  keep- 
ing the  same  time,  no  interference  of  the  one  with  the  other 


Fio.  20.— Horse  in  the  act  of  trotting.  In  this,  as  in  all  the  other  paces, 
tlie  body  of  the  horse  is  levered  forward  by  a  diagonal  twisting  of  the  trunk 
and  extremities,  the  extremities  describing  a  tigure-of-8  track  (s  u,  r  t). 
The  ligiire-of-8  is  produced  by  the  alternate  play  of  the  extremities  and  feet, 
two  of  which  are  always  on  the  ground  (a,  l>).  Thus  the  right  fore  foot  describes 
the  curve  marked  t,  the  left  hind  foot  that  marked  r,  the  left  fore  foot  that 
marked  v,  and  the  right  hind  loot  that  marked  s.  The  feet  on  the  ground  in 
the  present  instance  are  the  left  fore  and  the  right  hind.  Compare  with 
figs.  18  and  19,  pp.  37  and  39.  -  Original. 

occurs,  and  each  successive  hind  foot  as  it  is  implanted  forms 
a  new  diagonal  with  the  opposite  fore,  the  latter  forming  the 
front  of  the  parallel  in  one  instant,  and  one  of  the  diagonal 
positions  in  the  next :  while  in  the  case  of  the  hind,  they 
assume  the  diagonal  on  alighting  and  become  the  terminators 
of  the  parallel  in  the  last  part  of  their  action." 

In  the  trot,  according  to  Bishop,  the  legs  move  in  pairs 


42  ANIMAL  LOCOMOTION. 

diagonally.  The  same  leg  moves  rather  oftener  during  the 
same  period  in  trotting  than  in  walking,  or  as  six  to  five.  The 
velocity  acquired  by  moving  the  legs  in  pairs,  instead  of  con- 
secutively^ depends  on  the  circumstance  that  in  the  trot  each 
leg  rests  on  the  ground  during  a  short  interval,  and  swings 
during  a  long  one ;  whilst  in  walking  each  leg  swings  a  short, 
and  rests  a  long  period.  The  undulations  arising  from  the 
projection  of  the  trunk  in  the  trot  are  chiefly  in  the  vertical 
plane ;  in  the  walk  they  are  more  in  the  horizontal. 

The  gallop  has  been  erroneously  believed  to  consist  of  a 
series  of  bounds  or  leaps,  the  two  hind  legs  being  on  the 
ground  when  the  two  fore  legs  are  in  the  air,  and  vice  versa', 
there  being  a  period  when  all  four  are  in  the  air.  Thus 
Sainbell  in  his  "  Essay  on  the  Proportions  of  Eclipse,"  states 
"  that  the  gallop  consists  of  a  repetition  of  bounds,  or  leaps, 
more  or  less  high,  and  more  or  less  extended  in  proportion  to 
the  strength  and  lightness  of  the  animal."  A  little  reflection 
will  show  that  this  definition  of  the  gallop  cannot  be  the 
correct  one.  When  a  horse  takes  a  ditch  or  fence,  he  gathers 
himself  together,  and  by  a  vigorous  effort  (particularly  of  the 
hind  legs),  throws  himself  into  the  air.  This  movement 
requires  immense  exertion  and  is  short-lived.  It  is  not  in 
the  power  of  any  horse  to  repeat  these  bounds  for  more  than 
a  few  minutes,  from  which  it  follows  that  the  gallop,  which 
may  be  continued  for  considerable  periods,  must  differ  very 
materially  from  the  leap. 

The  pace  known  as  the  amble  is  an  artificial  movement, 
produced  by  the  cunning  of  the  trainer.  It  resembles  that  of 
the  giraffe,  where  the  right  for^p  and  right  hind  foot  move 
together  to  form  one  step ;  the"  left  fore  and  left  hind  foot 
Moving  together  to  form  the  second  step.  By  the  rapid 
repetition  of  these  movements  the  right  and  left  sides  of  the 
body  are  advanced  alternately  by  a  lateral  swinging  motion, 
very  comfortable  for  the  rider,  but  anything  but  graceful. 
The  amble  is  a  defective  pace,  inasmuch  as  it  interferes  with 
the  diagonal  movements  of  the  limbs,  and  impairs  the  con- 
tinuity of  motion  which  the  twisting,  cross  movement  begets. 
Similar  remarks  might  be  made  of  the  gallop  if  it  consisted 
(which  it  does  not)  of  a  series  of  bounds  or  leaps,  as  each 


PKOGRESSION  ON  THE  LAND.  43 

bound  would  be  succeeded  by  a  halt,  or  dead  point,  that  could 
not  fail  seriously  to  compromise  continuous  forward  motion. 
In  the  gallop,  as  in  the  slower  movements,  the  horse  has 
never  less  than  two  feet  on  the  ground  at  any  instant  of  time, 
no  two  of  the  four  feet  being  in  exactly  the  same  position. 

Mr.  Gamgee,  who  has  studied  the  movements  of  the  horse 
very  carefully,  has  given  diagrams  of  the  walk,  trot,  and 
gallop,  drawn  to  a  scale  of  the  feet  of  a  two-year-old  colt  in 
training,  which  had  been  walked,  trotted,  and  galloped  over 
the  ground  for  the  purpose.  The  point  he  sought  to  deter- 
mine was  the  exact  distance  through  which  each  foot  was 
carried  from  the  place  where  it  was  lifted  to  that  Avhere  it 
alighted.  The  diagrams  are  reproduced  at  figures  21,  22,  and 
23.  In  figure  231  have  added  a  continuous  waved  line  to 
indicate  the  alternating  movements  of  the  extremities  ;  Mr. 
Gamgee  at  the  time  he  wrote  L  being,  he  informs  me,  unac- 
quainted with  the  figure-of-8  theory  of  animal  progression  as 
subsequently  developed  by  me.  Compare  fig.  23  with  figs. 
18  and  19,  pp.  37  and  39  ;  with  fig.  50,  p.  97  ;  and  with  figs. 
71  and  73,  p.  144. 

WALK.  TROT. 

n.f.  n.h.      o.f.    o.h.      n.f.  n.f.  n.h.  o.f.      o.h.  n.f. 

-3)  q>      a  „.__.  s 


11  in.  23  in.  121  in.  18J  in.  19in.         42in.  21  in.  SOin. 

Length  of  stride  5  ft.  5  in.  Length  of  stride  10  ft  1  in. 

Fio.  21.  FIG.  22. 

GALLOP. 
n.f.  o.f.  n  h.  o.h.  n.f 


55}  in.  55  in.  55J  in.  55  in. 

Length  of  stride  IS  ft  1*  in. 

Fid.  23 

In  examining  figures  21,  22,  and  23,  the  reader  will  do 
well  to  remember  that  the  near  fore  and  hind  feet  of  a  horse 
are  the  left  fore  and  hind  feet ;  the  off  fore  and  hind  feet 
being  the  right  fore  and  hind  feet.  The  terms  near  and  off 

i  "  On  the  Breeding  of  Hunters  and  Roadsters."  Prize  Essay.— Journal  of 
Royal  Agricultural  Society  for  1863. 


44  ANIMAL  LOCOMOTION. 

are  technical  expressions,  and  apply  to  the  left  and  right 
sides  of  the  animal.  Another  point  to  be  attended  to  in 
examining  the  figures  in  question,  is  the  relation  which 
exists  between  the  fore  and  hind  feet  of  the  near  and 
off  sides  of  the  body.  In  slow  walking  the  near  hind  foot 
is  planted  behind  the  imprint  made  by  the  near  fore  foot. 
In  rapid  walking,  on  the  contrary,  the  near  hind  foot  is 
planted  from  six  to  twelve  or  more  inches  in  advance  of  the 
imprint  made  by  the  near  fore  foot  (fig.  21  represents 
the  distance  as  eleven  inches).  In  the  trot  the  near  hind  foot 
is  planted  from  twelve  to  eighteen  or  more  inches  in  advance  of 
the  imprint  made  by  the  near  fore  foot  (fig.  22  represents  the 
distance  as  nineteen  inches).  In  the  gallop  the  near  hind  foot 
is  planted  100  or  more  inches  in  advance  of  the  imprint  made 
by  the  near  fore  foot  (fig.  23  represents  the  distance  as  110J 
inches).  The  distance  by  which  the  near  hind  foot  passes 
the  near  fore  foot  in  rapid  walking,  trotting,  and  galloping, 
increases  in  a  progressive  ratio,  and  is  due  in  a  principal 
measure  to  the  velocity  or  momentum  acquired  by  the  mass 
of  the  horse  in  rapid  motion ;  the  body  of  the  animal  carrying 
forward  and  planting  the  limbs  at  greater  relative  distances 
in  the  trot  than  in  the  rapid  walk,  and  in  the  gallop  than  in 
the  trot.  I  have  chosen  to  speak  of  the  near  hind  and  near 
fore  feet,  but  similar  remarks  may  of  course  be  made  of  the 
off  hind  and  off  fore  feet. 

"At  fig.  23,  which  represents  the  gallop,  the  distance 
between  two  successive  impressions  produced,  say  by  the  near 
fore  foot,  is  eighteen  feet  one  inch  and  a  half.  Midway 
between  these  two  impressions  is  the  mark  of  the  near  hind 
foot,  which  therefore  subdivides  the  space  into  nine  feet  and 
six-eighths  of  an  inch,  but  each  of  these  is  again  subdivided 
into  two  halves  by  the  impressions  produced  by  the  off  fore 
and  off  hind  feet.  It  is  thus  seen  that  the  horse's  body 
instead  of  being  propelled  through  the  air  by  bounds  or  leaps 
«v«n  when  going  at  the  highest  attainable  speed,  acts  on  a 
system  of  levers,  the  mean  distance  between  the  points  of 
resistance  of  which  is  four  feet  six  inches.  The  exact  length 
of  stride,  of  course,  only  applies  to  that  of  the  particular  horse 
observed,  and  the  rate  of  speed  at  which  he  is  going.  In  the 


PROGRESSION  ON  THE  LAND.  45 

case  of  any  one  animal,  the  greater  the  speed  the  longer  is 
the  individual  stride.  In  progression,  the  body  moves  before  a 
limb  is  raised  from  the  ground,  as  is  most  readily  seen  when 
the  horse  is  beginning  its  slowest  action,  as  in  traction."  * 

At  fig.  22,  which  represents  the  trot,  the  stride  is  ten  feet 
one  inch.  At  'fig.  21,  which  represents  the  walk,  it  is  only 
five  feet  five  inches.  The  speed  acquired,  Mr.  Gamgee  points 
out,  determines  the  length  of  stride;  the  length  of  stride 
being  the  effect  and  evidence  of  speed  and  not  the  cause  of  it. 
The  momentum  acquired  in  the  gallop,  as  already  explained, 
greatly  accelerates  speed. 

"  In  contemplating  length  of  strides,  with  reference  to  the 
fulcra,  allowance  has  to  be  made  for  the  length  of  the  feet, 
which  is  to  be  deducted  from  that  of  the  strides,  because  the 
apex,  or  toe  of  the  horse's  hind  foot  forms  the  fulcrum  in  one 
instant,  and  the  heel  of  the  fore  foot  in  the  next,  and  vice 
versd.  This  phenomenon  is  very  obvious  in  the  action  of  the 
human  foot,  and  is  remarkable  also  for  the  range  of  leverage 
thus  afforded  in  some  of  the  fleetest  quadrupeds,  of  different 
species.  In  the  hare,  for  instance,  between  the  point  of  its 
hock  and  the  termination  of  its  extended  digits,  there  is  a 
space  of  upwards  of  six  inches  of  extent  of  leverage  and 
variation  of  fulcrum,  and  in  the  fore  limb  from  the  carpus  to 
the  toe-nails  (whose  function  in  progression  is  not  to  be 
underrated)  upwards  of  three  inches  of  leverage  are  found, 
being  about  ten  inches  for  each  lateral  biped,  and  the  double 
of  that  for  the  action  of  all  four  feet.  Viewed  in  this  way 
the  stride  is  not  really  so  long  as  would  be  supposed  if  merely 
estimated  from  the  space  between  the  footprints. 

Many  interesting  remarks  might  be  made  on  the  length  of 
the  stride  of  various  animals ;  the  full  movement  of  the  grey- 
hound is,  for  instance,  upwards  of  sixteen  feet ;  that  of  the 
har.e  at  least  equal ;  whilst  that*  of  the  Newfoundland  dog  is 
a  little  over  nine  feet." l 

Locomotion  of  the  Ostrich. — Birds  have  been  divided  by 
naturalists  into  eight  orders : — the  Natatores,  or  Swimming 
Birds ;  the  Grallatores,  or  Wading  Birds ;  the  Cursores,  or 
Running  Birds ;  the  Scansores,  or  Climbers ;  the  Easores,  or 

i  Gamgee  in  Journal  of  Anatomy  and  Physiology,  vol.  iii.  pp.  375,  37Q. 


46  ANIMAL  LOCOMOTION. 

Scrapers;  the  Columbw,  or  Doves;  the  Passeres ;  and  the 
Raptor es,  or  Birds  of  Prey. 

The  first  five  orders  have  been  classified  according  to  their 
habits  and  modes  of  progression.  The  Natatores  I  shall  con- 
sider when  I  come  to  speak  of  swimming  as  a  form  of  locomo- 
tion, and  as  there  is  nothing  in  the  movements  of  the  wading, 
scraping,  and  climbing  birds,1  or  in  the  Passeres  2  or  fiaptores, 
requiring  special  notice,  I  shall  proceed  at  once  to  a  considera- 
tion of  the  Cursores,  the  best  examples  of  which  are  the 
ostrich,  emu,  cassowary,  and  apteryx. 

The  ostrich  is  remarkable  for  the  great  length  and  develop- 
ment of  its  legs  as  compared  with  its  wings  (fig.  24).  In  this 
respect  it  is  among  birds  what  the  kangaroo  is  among  mammals. 
The  -ostrich  attains  an  altitude  of  from  six  to  eight  feet,  and 
is  the  largest  living  bird  known.  Its  great  height  is  due  to 
its  attenuated  neck  and  legs.  The  latter  are  very  powerful 
structures,  and  greatly  resemble  in  their  general  conformation 
the  posterior  extremities  of  a  thoroughbred  horse  or  one  of  the 
larger  deer — compare  with  fig.  4,  p.  21.  They  are  expressly 
made  for  speed.  Thus  the  bones  of  the  leg  and  foot  are  in- 
clined very  obliquely  towards  each  other,  the  femur  being  in- 
clined very  obliquely  to  the  ilium.  As  a  consequence  the 
angles  made  by  the  several  bones  of  the  legs  are  compara- 
tively small ;  smaller  in  fact  than  in  either  the  horse  or  deer. 

The  feet  of  the  ostrich,  like  those  of  the  horse  and  deer, 
are  reduced  to  a  minimum  as  regards  size;  so  that  they 
occasion  very  little  friction  in  the  act  of  walking  and  running. 
The  foot  is  composed  of  two  jointed  toes,3  which  spread  out 
when  the  weight  of  the  body  comes  upon  them,  in  such  a 
manner  as  enables  the  bird  to  seize  and  let  go  the  ground 
with  equal  facility.  The  advantage  of  such  an  arrangement 
in  rapid  locomotion  cannot  be  over-estimated.  The  elasticity 
and  flexibility  of  the  foot  contribute  greatly  to  the  rapidity 

1  The  woodpeckers  climb  by  the  aid  of  the  stiff  feathers  of  their  tails ;  the 
legs  and  tail  forming  a  firm  basis  of  support. 

*  In  this  order  there  are  certain  birds — the  sparrows  and  thrushes,  for 
example— which  advance  by  a  series  of  vigorous  leaps  ;  the  leaps  b°.ing  of  an 
intermitting  character. 

3-The  toes  in  the  emu  amount  to  three. 


PROGRESSION  ON  THE  LAND. 


47 


of  movement  for  which  this  celebrated  bird  is  famous.  The 
limb  of  the  ostrich,  with  its  large  bones  placed  very  obliquely 
to  form  a  system  of  powerful  levers,  is  the  very  embodiment 
of  speed.  The  foot  is  quite  worthy  of  the  limb,  it  being  in 


Fi<;.  24.— Skeleton  of  the  Ostrich.  Shows  the  powerful  legs,  small  feet,  anil 
rudimentary  wings  of  the  bird  :  the  obliquity  at  which  the  bones  of  the  legs 
and  wings  are  placed,  and  the  comparatively  small  angles  which  any  two 
bones  make  at  tlu-ir  point  of  junction,  a  Angle  made  by  femur  with  ilium. 
b  Angle  made  by  tibia  and  fibula  with  femur,  c  Angle  made  by  tarso- 
metatarsal  bone  with  tibia  and  fibula,  d  Angle  made  by  bones  of  foot  with 
tarso-metatarsnl  bone,  r  Bones  of  wing  inclined  to  each  other  at  nearly  right 
angles.  Compare  with  fig.  4,  p.  21,  fig.  26,  p.  55,  and  fig.  27,  p.  59.— Adapted 
from  Dallas. 

some  respects  the  most  admirable  structure  of  its  kind  in 
existence.  The  foot  of  the  ostrich  differs  considerably  from 
that  of  all  other  birds,  thosie  of  its  own  family  excepted. 
Thus  the  .under  portion  of  the  foot  is  flat,  and  specially 
adapted  for  acting  on  plane  surfaces,  particularly  solids.1  The 

1  Feet  designed  for  swimming,  grasping  trees,  or  securing  prey,  do  not 
operate  to  advantage  on  a  flat  surface.  The  awkward  waddle  of  the  swan, 
parrot,  and  eagle  when  on  the  ground  affords  illustrations. 


48  ANIMAL  LOCOMOTION. 

extremities  of  the  toes  superiorly  are  armed  with  powerful 
short  nails,  the  tips  of  which  project  inferiorly  to  protect  the 
toes  and  confer  elasticity  when  the  foot  is  leaving  the  ground. 
The  foot,  like  the  leg,  is  remarkable  for  its  great  strength. 
The  legs  of  the  ostrich  are  closely  set,  another  feature  of 
speed.1  The  wings  of  the  ostrich  are  in  a  very  rudimentary 


Fio.  25. — Ostriches  pursued  by  a  Hunter. 

condition  as  compared  with  the  legs.2  All  the  bones  are  pre- 
sent, but  they  are  so  dwarfed  that  they  are  useless  as  organs 
of  flight.  The  angles  which  the  bones  of  the  wing  make  with 
each  other,  are  still  less  than  the  angles  made  by  the  bones  of 
the  leg.  This  is  just  what  we  would  a  priori  expect,  as  the 
velocity  with  which  wings  are  moved  greatly  exceeds  that 
with  which  legs  are  moved.  The  bones  of  the  wing  of  the 
ostrich  are  inclined  towards  each  other  at  nearly  right  angles. 

1  In  draught  horses  the  legs  are  much  wider  apart  than  in  racers  ;  the  legs 
of  the  deer  being  less  widely  set  than  those  of  the  racer. 

*  In  the  apteryx  the  wings  are  so  very  small  that  the  bird  is  commonly 
spoken  of  as  the  "  wingless  bird." 


PROGRESSION  ON  THE  LAND.  49 

The  wings  of  the  ostrich,  although  useless  as  flying  organs, 
form  important  auxiliaries  in  running.  When  the  ostrich 
careers  along  the  plain,  he  spreads  out  his  wings  in  such  a 
manner  that  they  act  as  balancers,  and  so  enable  him  to  main- 
tain his  equilibrium  (fig.  25).  The  wings,  because  of  the  angle  of 
inclination  which  their  under  surfaces  make  with  the  horizon, 
and  the  great  speed  at  which  the  ostrich  travels,  act  like 
kites,  and  so  elevate  and  carry  forward  by  a  mechanical 
adaptation  a  certain  proportion  of  the  mass  of  the  bird 
already  in  motion.  The  elevating  and  propelling  power  of 
even  diminutive  inclined  planes  is  very  considerable,  when 
carried  along  at  a  high  speed  in  a  horizontal  direction.  The 
wings,  in  addition  to  their  elevating  and  propelling  power, 
contribute  by  their  short,  rapid,  swinging  movements,  to  con- 
tinuity of  motion  in  the  legs.  No  bird  with  large  wings  can 
run  well.  The  albatross,  for  example,  walks  with  difficulty, 
and  the  same  may  be  said  of  the  vulture  and  eagle.  What, 
therefore,  appears  a  defect  in  the  ostrich,  is  a  positive  advan- 
tage when  its  habits  and  mode  of  locomotion  are  taken  into 
account. 

Professional  runners  in  many  cases  at  matches  reduce  the 
length  of  their  anterior  extremities  by  flexing  their  arms  and 
carrying  them  on  a  level  with  their  chest  (fig.  28,  p.  62).  It 
would  seem  that  in  rapid  running  there  is  not  time  for  the  arms 
to  oscillate  naturally,  and  that  under  these  circumstances  the 
arms,  if  allowed  to  swing  about,  retard  rather  than  increase 
the  spe<sd.  The  centre  of  gravity  is  well  forward  in  the 
ostrich,  and  is  regulated  by  the  movements  of  the  head  and 
neck,  and  the  obliquity  of  the  body  and  legs.  In  running 
the  neck  is  stretched,  the  body  inclined  forward,  and  the  legs 
moved  alternately  and  with  great  rapidity.  When  the  right 
leg  is  flexed  and  elevated,  it  swings  fonvard  pendulum- 
fashion,  and  describes  a  curve  whose  convexity  is  directed 
towards  the  right  side.  When  the  left  leg  is  flexed  and 
elevated,  it  swings  forward  and  describes  a  curve  whose  con- 
vexity is  directed  towards  the  left  side.  The  curves  made  by 
the  right  and  left  legs  form  when  united  a  waved  line  (vide 
figs.  18,  19,  and  20,  pp.  37,  39,  and  41).  When  the  right 
leg  is  flexed,  elevated,  and  advanced,  it  rotates  upon  the  iliac 


50  ANIMAL  LOCOMOTION. 

portion  of  the  trunk  of  the  bird,  the  trunk  being  supported 
for  the  time  being  by  the  left  leg,  which  is  extended,  and  in 
contact  with  the  ground.  When  the  left  leg  is  flexed,  elevated, 
and  advanced,  it  in  like  manner  rotates  upon  the  trunk,  sup- 
ported in  this  instance  by  the  extended  right  leg.  The  leg 
which  is  on  the  ground  for  the  time  being  supplies  the  neces- 
sary lever,  the  ground  the  fulcrum.  When  the  right  leg  is 
flexed  and  elevated,  it  rotates  upon  the  iliac  portion  of  the 
trunk  in  a  forward  direction,  the  right  foot  describing  the  arc  of 
a  circle.  When  the  right  leg  and  foot  are  extended  and  fixed 
on  the  ground,  the  trunk  rotates  upon  the  right  foot  in  a  for- 
ward direction  to  form  the  arc  of  a  circle,  which  is  the  converse 
of  that  formed  by  the  right  foot.  If  the  arcs  alternately  supplied 
by  the  right  foot  and  trunk  are  placed  in  opposition,  a  more 
or  less  perfect  circle  is  produced,  and  thus  it  is  that  the  loco- 
motion of  animals  is  approximated  to  the  wheel  in  mechanics. 
Similar  remarks  are  to  be  made  of  the  left  foot  and  trunk. 
The  alternate  rolling  of  the  trunk  on  the  extremities,  and  the 
extremities  on  the  trunk,  utilizes  or  works  up  the  inertia  of  the 
moving  mass,  and  powerfully  contributes  to  continuity  and 
steadiness  of  action  in  the  moving  parts.  By  advancing  the  head, 
neck,  and  anterior  parts  of  the  body,  the  ostrich  inaugurates 
the  rolling  movement  of  the  trunk,  which  is  perpetuated  by 
the  rolling  movements  of  the  legs.  The  trunk  and  legs  of  the 
ostrich  are  active  and  passive  by  turns.  The  movements  of 
the  trunk  and  limbs  are  definitely  co-ordinated.  But  for  this 
reciprocation  the  action  of  the  several  parts  implicated  would 
neither  be  so  rapid,  certain,  nor  continuous.  The  speed  of 
the  ostrich  exceeds  that  of  every  other  land  animal,  a  circum- 
stance due  to  its  long,  powerful  legs  and  great  stride.  It  can 
outstrip  without  difficulty  the  fleetest  horses,  and  is  only 
captured  by  being  simultaneously  assailed  from  various  points, 
or  run  down  by  a  succession  of  hunters  on  fresh  steeds. 
If  the  speed  of  the  ostrich,  which  only  measures  six  or  eight 
feet,  is  so  transcending,  what  shall  we  say  of  the  speed  of  the 
extinct  JEpyornis  maximus  and  Dinornis  giganteus,  which  are 
supposed  to  have  measured  from  sixteen  to  eighteen  feet  in 
height?  Incredible  as  it  may  appear,  the  ostrich,  with  its 
feet  reduced  to  a  minimum  as  regards  size,  and  peculiarly 


PROGRESSION  ON  THE  LAND.  51 

organized  for  walking  and  running  on  solids,  can  also  swim. 
Mr.  Darwin,  that  most  careful  of  all  observers,  informs  us 
that  ostriches  take  to  the  water  readily,  and  not  only  ford 
rapid  rivers,  but  also  cross  from  island  to  island.  They  swim 
leisurely,  with  neck  extended,  and  the  greater  part  of  the 
body  submerged. 

Locomotion  in  Man. — The  speed  attained  by  man,  although 
considerable,  is  not  remarkable.  It  depends  on  a  variety  of 
circumstances,  -such  as  the  height,  age,  sex,  and  muscular 
energy  of  the  individual,  the  nature  of  the  surface  passed 
over,  and  the  resistance  to  forward  motion  due  to  the  presence 
of  air,  whether  still  or  moving.  A  reference  to  the  human 
skeleton,  particularly  its  inferior  extremities,  will  explain  why 
the  speed  should  be  moderate. 

On  comparing  the  inferior  extremities  of  man  with  the  legs 
of  birds,  or  the  posterior  extremities  of  quadrupeds,  say  the 
horse  or  deer,  we  find  that  the  bones  composing  them  are  not 
so  obliquely  placed  with  reference  to  each  other,  neither  are 
the  angles  formed  by  any  two  bones  so  acute.  Further,  we 
observe  that  in  birds  and  quadrupeds  the  tarsal  and  meta- 
tarsal  bones  are  so  modified  that  there  is  an  actual  increase 
in  the  number  of  the  angles  themselves.  In  the  extremities 
of  birds  and  quadrupeds  there  are  four  angles,  which  may  bo 
increased  or  diminished  in  the  operations  of  locomotion. 
Thus,  in  the  quadruped  and  bird  (fig.  4,  p.  21,  and  fig.  24,  p. 
47),  the  femur  forms  with  the  ilium  one  angle  (a)  ;  the  tibia 
and  fibula  with  the  femur  a  second  angle  (V) ;  the  cannon  or 
tarso-metatarsal  bone  with  the  tibia  and  fibula  a  third  angle 
(c) ;  and  the  bones  of  the  foot  with  the  cannon  or  tarso-meta- 
tarsal bone  a  fourth  angle  (d).  In  man  three  angles  only  are 
found,  marked  respectively  a,  b,  and  c  (figs.  26  and  27,  pp.  55 
and  59).  The  fourth  angle  (d  of  figs.  4  and  24)  is  absent. 
The  absence  of  the  fourth  angle  is  due  to  the  fact  that  in  man 
the  tarsal  and  metatarsal  bones  are  shortened  and  crushed 
together;  whereas  in  the  quadruped  and  bird  they  are  elon- 
gated and  separated. 

As  the  speed  of  a  limb  increases  in  proportion  to  the  num- 
ber and  acuteness  of  the  angles  formed  by  its  several  bones,  it 
is  not  difficult  to  understand  why  man  should  not  be  so  swift 


52  ANIMAL  LOCOMOTION. 

as  the  majority  of  quadrupeds.  The  increase  in  the  number 
of  angles  increases  the  power  which  an  animal  has  of  shorten- 
ing and  elongating  its  extremities,  and  the  levers  which  the 
extremities  form.  To  increase  the  length  of  a  lever  is  to 
increase  its  power  at  one  end,  and  the  distance  through  which 
it  moves  at  the  other ;  hence  the  faculty  of  bounding  or  leap- 
ing possessed  in  such  perfection  by  many  quadrupeds.1  If 
the  wing  be  considered  as  a  lever,  a  small  degree  of  motion  at 
its  root  produces  an  extensive  sweep  at  its  tip.  It  is  thus 
that  the  wing  is  enabled  to  work  up  and  utilize  the  thin 
medium  of  the  air  as  a  buoying  medium. 

Another  drawback  to  great  speed  in  man  is  his  erect  posi- 
tion. Part  of  the  power  which  should  move  the  limbs  is 
dedicated  to  supporting  the  trunk.  For  the  same  reason  the 
bones  of  the  legs,  instead  of  being  obliquely  inclined  to  each 
other,  as  in  the  quadruped  and  bird,  are  arranged  in  a  nearly 
vertical  spiral  line.  This  arrangement  increases  the  angle 
formed  by  any  two  bones,  and,  as  a  consequence,  decreases 
the  speed  of  the  limbs,  as  explained.  A  similar  disposition  of 
the  bones  is  found  in  the  anterior  extremities  of  the  elephant, 
where  the  superincumbent  weight  is  great,  and  the  speed, 
comparatively  speaking,  not  remarkable.  The  bones  of  the 
human  leg  are  beautifully  adapted  to  sustain  the  weight  of 
the  body  and  neutralize  shock.2  Thus  the  femur  or  thigh 
bone  is  furnished  at  its  upper  extremity  with  a  ball-and-socket 
joint  which  unites  it  to  the  cup-shaped  depression  (acetabu- 
lum)  in  the  ilium  (hip  bone).  It  is  supplied  with  a  neck 
which  carries  the  body  or  shaft  of  the  bone  in  an  oblique 
direction  from  the  ilium,  the  shaft  being  arched  forward  and 
twisted  upon  itself  to  form  an  elongated  cylindrical  screw. 
The  lower  extremity  of  the  femur  is  furnished  with  spiral 
articular  surfaces  accurately  adapted  to  the  upper  extremities 
of  the  bones  of  the  leg,  viz.  the  tibia  and  fibula,  and  to  the 
patella.  The  bones  of  the  leg  (tibia  and  fibula)  are  spirally 

1  "  The  posterior  extremities  in  both  the  lion  and  tiger  are  longer,  and  the 
bones  inclined  more  obliquely  to  each  other  than  the  anterior,  giving  them 
greater  power  and  elasticity  in  springing." 

"  The  pelvis  receives  the  whole  weight  of  the  trunk  and  superposed 
organs,  and  transmits  it  tn  the  heads  of  the  femurs." 


PROGRESSION  ON  THE  LAND.  63 

arranged,  the  screw  in  this  instance  being  split  up.  At  the 
ankle  the  bones  of  the  leg  are  applied  to  those  of  the  foot  by 
spiral  articular  surfaces  analogous  to  those  found  at  the  knee- 
joint.  The  weight  of  the  trunk  is  thus  thrown  on  the  foot, 
not  in  straight  lines,  but  in  a  series  of  curves.  The  foot 
itself  is  wonderfully  adapted  to  receive  the  pressure  from 
above.  It  consists  of  a  series  of  small  bones  (the  tarsal, 
metatarsal,  and  phalangeal  bones),  arranged  in  the  form  of  a 
double  arch ;  the  one  arch  extending  from  the  heel  towards 
the  toes,  the  other  arch  across  the  foot.  The  foot  is  so  con- 
trived that  it  is  at  once  firm,  elastic,  and  moveable, — qualities 
which  enable  it  to  sustain  pressure  from  above,  and  exert 
pressure  from  beneath.  In  walking,  the  heel  first  reaches 
and  first  leaves  the  ground.  When  the  heel  is  elevated  the 
weight  of  the  body  falls  more  and  more  on  the  centre  of 
the  foot  and  toes,  the  latter  spreading  out l  as  in  birds,  to 
seize  the  ground  and  kver  the  trunk  forward.  It  is  in  this 
movement  that  the  wonderful  mechanism  of  the  foot  is  dis- 
played to  most  advantage,  the  multiplicity  of  joints  in  the 
foot  all  yielding  a  little  to  confer  that  elasticity  of  step  which 
is  so  agreeable  to  behold,  and  which  is  one  of  the  character- 
istics of  youth.  The  foot  may.be  said  to  roll  over  the  ground 
in  a  direction  from  behind  forwards.  I  have  stated  that  the 
angles  formed  by  the  bones  of  the  human  leg  are  larger  than 
those  formed  by  the  bones  of  the  leg  of  the  quadruped  and  bird. 
This  is  especially  true  of  the  angle  formed  by  the  femur  with 
the  ilium,  which,  because  of  the  upward  direction  given  to  the 
crest  of  the  ilium  in  man,  is  so  great  that  it  virtually  ceases 
to  be  an  angle. 

The  bones  of  the  superior  extremities  in  man  merit  atten- 
tion from  the  fact  that  in  walking  and  running  they  oscillate 
in  opposite  directions,  and  alternate  and  keep  time  with  the 
less,  which  oscillate  in  a  similar  manner.  The  arms  are  arti- 

0  * 

culated  at  the  shoulders  by  ball-and-socket  joints  to  cup-shaped 
depressions  (glenoid  cavities)  closely  resembling  those  found  at 
the  hip-joints.  The  bone  of  the  arm  (humerus)  is  carried  away 

1  The  spreading  action  of  the  toes  is  seen  to  perfection  in  children.     It  is 
more  or  less  destroyed  in  adults  from  a  faulty  principle  in  boot  and  shoemak- 
ing,  the  soles  being  invariably  too  narrow. 


54  ANIMAL  LOCOMOTION. 

from  the  shoulder  by  a  short  neck,  as  in  the  thigh-bone  (femur). 
Like  the  thigh-bone  it  is  twisted  upon  itself  and  forms  a  screw. 
The  inferior  extremity  of  the  arm  bone  is  furnished  with 
spiral  articular  surfaces  resembling  those  found  at  the  knee. 
The  spiral  articular  surfaces  of  the  arm  bone  are  adapted  to 
similar  surfaces  existing  on  the  superior  extremities  of  the 
bones  of  the  forearm,  to  wit,  the  radius  and  ulna.  These 
bones,  like  the  bones  of  the  leg,  are  spirally  disposed  with 
reference  to  each  other,  and  form  a  screw  consisting  of  two 
parts.  The  bones  of  the  forearm  are  united  to  those  of 
the  wrist  (carpal)  and  hand  (metacarpal  and  phalangeal)  by 
articular  surfaces  displaying  a  greater  or  less  degree  of 
spirality.  From  this  it  follows  that  the  superior  extremities 
of  man  greatly  resemble  his  inferior  ones ;  a  fact  of  consider- 
able importance,  as  it  accounts  for  the  part  taken  by  the 
superior  extremities  in  locomotion.  In  man  the  arms  do  not 
touch  the  ground  as  in  the  brutes,  but  they  do  not  on  this 
account  cease  to  be  useful  as  instruments  of  progression.  If 
a  man  walks  with  a  stick  in  each  hand  the  movements  of  his 
extremities  exactly  resemble  those  of  a  quadruped. 

The  bones  of  the  human  extremities  (superior  and  inferior) 
are  seen  to  advantage  in  fig.  26;  and  I  particularly  direct 
the  attention  of  the  reader  to  the  ball-and-socket  or  universal 
joints  by  which  the  arms  are  articulated  to  the  shoulders 
(x,  x'),  and  the  legs  to  the  pelvis  (a,  aT),  as  a  knowledge  of 
these  is  necessary  to  a  comprehension  of  the  oscillating  or 
pendulum  movements  of  the  limbs  now  to  be  described.  The 
screw  configuration  of  the  limbs  is  well  depicted  in  the  left 
arm  (x)  of  the  present  figure.  Compare  with  the  wing  of  the 
bird,  fig.  6,  and  with  the  anterior  extremity  of  the  elephant, 
fig.  7,  p.  28.  But  for  the  ball-and-socket  joints,  and  the 
spiral  nature  of  the  bones  and  articular  surfaces  of  the  extre- 
mities, the  undulating,  sinuous,  and  more  or  less  continuous 
movements  observable  in  walking  and  running,  and  the 
twisting,  lashing,  flail-like  movements  necessary  to  swimming 
and  flying,  would  be  impossible. 

The  leg  in  the  human  subject  moves  by  three  joints,  viz., 
the  hip,  knee,  and  ankle  joints.  When  standing  in  the  erect 
position,  the  hip-joint  only  permits  the  limb  to  move  forwards, 


PROGRESSION  ON  THE  LAND. 


55 


the  knee-joint  backwards,  and  the  ankle-joint  neither  back- 
wards nor  forwards.     When  the  body  or  limbs  are  inclined 


Fid.  26.— Skeleton  of  Man.     Compare  with  fig.  4,  p.  21,  and  fig.  24,  p.  47. — Original. 

obliquely,  or  slightly  flexed,  the  range  of  motion  is  increased. 


56  ANIMAL  LOCOMOTION. 

The  greatest  angle  made  at  the  knee-joint  is  equal  to  the 
Bums  of  the  angles  made  by  the  hip  and  ankle  joints  when 
these  joints  are  simultaneously  flexed,  and  when  the  angle  of 
inclination  made  by  the  foot  with  the  ground  equals  30°. 

From  this  it  follows  that  the  trunk  maintains  its  erect 
position  during  the  extension  and  flexion  of  the  limbs.  The 
step  in  walking  was  divided  by  Borelli  into  two  periods,  the 
one  corresponding  to  the  time  when  both  limbs  are  on  the 
ground ;  the  other  when  only  one  limb  is  on  the  ground.  In 
running,  there  is  a  brief  period  when  both  limbs  are  off  the 
ground.  In  walking,  the  body  is  alternately  supported  by 
the  right  and  left  legs,  and  advanced  by  a  sinuous  movement. 
Its  forward  motion  is  quickened  when  one  leg  is  on  the 
ground,  and  slowed  when  both  are  on  the  ground.  When 
the  limb  (say  the  right  leg)  is  flexed,  elevated,  and  thrown 
forward,  it  returns  if  left  to  itself  (i.e.  if  its  movements  are 
not  interfered  with  by  the  voluntary  muscles)  to  the  position 
from  which  it  was  moved,  viz.  the  vertical,  unless  the  trunk 
bearing  the  limb  is  inclined  in  a  forward  direction  at  the 
same  time.  The  limb  return*  to  the  vertical  position,  or 
position  of  rest,  in  virtue  of  the  power  exercised  by  gravity, 
and  from  its  being  hinged  at  the  hip  by  a  ball-and-socket 
joint,  as  explained.  In  this  respect  the  human  limb  when 
allowed  to  oscillate  exactly  resembles  a  pendulum, — a  fact  first 
ascertained  by  the  brothers  Weber.  The  advantage  accruing 
from  this  arrangement,  as  far  as  muscular  energy  is  concerned, 
is  very  great,  the  muscles  doing  comparatively  little  work.1 
In  beginning  to  walk,  the  body  and  limb  which  is  to  take 
the  first  step  are  advanced  together.  When,  however,  the 
body  is  inclined  forwards,  a  large  proportion  of  the  step  is 
performed  mechanically  by  the  tendency  which  the  pendulum 
formed  by  the  leg  has  to  swing  forward  and  regain  a  vertical 
position, — an  effect  produced  by  the  operation  of  gravity  alone. 
The  leg  which  is  advanced  swings  further  forward  than  is 
required  for  the  step,  and  requires  to  swing  back  a  little 
before  it  can  be  deposited  on  the  ground.  The  pendulum 

1  The  brothers  Weber  found  that  so  long  as  the  muscles  exert  the  general 
force  necessary  to  execute  locomotion,  the  velocity  depends  on  the  size  of  the 
legs  and  on  external  forces,  but  not  on  the  strength,  of  the  muscles. 


PROGRESSION  ON  THE  LAND.  57 

movement  effects  all  this  mechanically.  When  the  limb  has 
swung  forward  as  far  as  the  inclination  of  the  body  at  the 
time  will  permit,  it  reverses  pendulum  fashion;  the  back 
stroke  of  the  pendulum  actually  placing  the  foot  upon  the 
ground  by  a  retrograde,  descending  movement.  When  the 
right  leg  with  which  we  commenced  is  extended  and  firmly 
placed  upon  the  ground,  and  the  trunk  has  assumed  a  nearly 
vertical  position,  the  left  leg  is  flexed,  elevated,  and  the  trunk 
once  more  bent  forward.  The  forward  inclination  of  the 
trunk  necessitates  the  swinging  forward  of  the  left  leg,  which, 
when  it  has  reached  the  point  permitted  by  the  pendulum 
movement,  swings  back  again  to  the  extent  necessary  to  place 
it  securely  upon  the  ground.  These  movements  are  repeated 
at  stated  and  regular  intervals.  The  retrograde  movement  of 
the  limb  is  best  seen  in  slow  walking.  In  fast  walking  the 
pendulum  movement  is  somewhat  interrupted  from  the  limb 
being  made  to  touch  the  ground  when  it  attains  a  vertical 
position,  and  therefore  before  it  has  completed  its  oscillation.1 
The  swinging  forward  of  the  body  may  be  said  to  inaugurate 
the  movement  of  walking.  The  body  is  slightly  bent  and 
inclined  forwards  at  the  beginning  of  each  step.  It  is 
straightened  and  raised  towards  the  termination  of  that  act. 
The  movements  of  the  body  begin  and  terminate  the  steps, 
and  in  this  manner  regulate  them.  The  trunk  rises  vertically 
at  each  step,  the  head  describing  a  slight  curve  well  seen  in 
the  walking  of  birds.  The  foot  on  the  ground  (say  the  right 
foot)  elevates  the  trunk,  particularly  its  right  side,  and  the 
weight  of  the  trunk,  particularly  its  left  side,  depresses  the 
left  or  swinging  foot,  and  assists  in  placing  it  on  the  ground. 
The  trunk  and  limbs  are  active  and  passive  by  turns.  In 
walking,  a  spiral  wave  of  motion,  most  marked  in  an  antero- 
posterior  direction  (although  also  appearing  laterally),  runs 
through  the  spine.  This  spiral  spinal  movement  is  observ- 
able in  the  locomotion  of  all  vertebrates.  It  is  favoured  in 
man  by  the  antero-posterior  curves  (cervical,  dorsal,  and  lum- 
bar) existing  in  the  human  vertebral  column.  In  the  effort 
of  walking  the  trunk  and  limbs  oscillate  on  the  ilio-femoral 

1  "  In  quick  walking  and  running  the  swinging  leg  never  passes  beyond 
the  vertical  which  nuts  the  head  of  the  femur." 
4 


58  ANIMAL  LOCOMOTION. 

articulations  (hip-joints).  The  trunk  also  rotates  in  a  forward 
direction  on  the  foot  which  is  placed  upon  the  ground  for  the 
time  being.  The  rotation  begins  at  the  heel  and  terminates 
at  the  toes.  So  long  as  the  rotation  continues,  the  body  rises. 
When  the  rotation  ceases  and  one  foot  is  placed  flat  upon  the 
ground,  the  body  falls.  The  elevation  and  rotation  of  the 
body  in  a  forward  direction  enables  the  foot  which  is  off 
the  ground  for  the  time  being  to  swing  forward  pendulum 
fashion ;  the  swinging  foot,  when  it  can  oscillate  no  further 
in  a  forward  direction,  reversing  its  course  and  retrograd- 
ing to  a  slight  extent,  at  which  juncture  it  is  deposited  on 
the  ground,  as  explained.  The  retrogression  of  the  swinging 
foot  is  accompanied  by  a  slight  retrogression  on  the  part  of 
the  body,  which  tends  at  this  particular  instant  to  regain  a 
vertical  position.  From  this  it  follows  that  in  slow  Avalking 
the  trunk  and  the  swinging  foot  advance  together  through  a 
considerable  space,  and  retire  through  a  smaller  space ;  that 
when  the  body  is  swinging  it  rotates  upon  the  ilio-femoral 
articulations  (hip-joints)  as  an  axis ;  and  that  when  the  leg 
is  not  swinging,  but  fixed  by  its  foot  upon  the  ground,  the 
trunk  rotates  upon  the  foot  as  an  axis.  These  movements 
are  correlated  and  complementary  in  their  nature,  and  are 
calculated  to  relieve  the  muscles  of  the  legs  and  trunk  en- 
gaged in  locomotion  from  excessive  wear  and  tear. 

Similar  movements  occur  in  the  arms,  which,  as  has  been 
explained,  are  articulated  to  the  shoulders  by  ball-and-socket 
joints  (fig.  26,  a;  x',  p.  55).  The  right  leg  and  left  arm  advance 
together  to  make  one  step,  and  so  of  the  left  leg  and  right 
arm.  When  the  right  leg  advances  the  right  arm  retires,  and 
vice  versd.  When  the  left  leg  advances  the  left  arm  retires, 
and  the  converse.  There  is  therefore  a  complementary  swing- 
ing of  the  limbs  on  each  side  of  the  body,  the  leg  swinging 
always  in  an  opposite  direction  to  the  arm  on  the  same  side. 
There  is,  moreover,  a  diagonal  set  of  movements,  also  com- 
plementary in  character  :  the  right  leg  and  left  arm  advancing 
together  to  form  one  step  ;  the  left  leg  and  right  arm  advanc- 
ing together  to  form  the  next.  The  diagonal  movements 
beget  a  lateral  twisting  of  the  trunk  and  limbs ;  the  oscilla- 
tion of  the  trunk  upon  the  limbs  or  feet,  and  the  oscillation 


PROGRESSION  ON  THE  LAND. 


59 


of  the  feet  and  limbs  upon  the  trunk,  generate  a  forward 
wave  movement,  accompanied  by  a  certain  amount  of  veiiical 
undulation.  The  diagonal  movements  of  the  trunk  and 
extremities  are  accompanied  by  a  certain  degree  of  lateral 
curvature ;  the  right  leg  and  left  arm,  when  they  advance  to 
make  a  step,  each  describing  a  curve,  the  convexity  of  which 
is  directed  to  the  right  and  left  respectively.  Similar  curves 
are  described  by  the  left  leg  and  right  arm  in  making  the 
second  or  complementary  step.  When  the  curves  formed  by 
the  right  and  left  legs  or  the  right  and  left  arms  are  joined, 
they  form  waved  tracks  symmetrically  arranged  on  either 
side  of  a  given  line.  The  curves  formed  by  the  legs  and 


FIG.  27  shows  the  simultaneous  positions  of  both  legs  during  a  step,  divided 
into  four  groups.  The  first  group  (^1),  4  to  7,  gives  the  different  positions 
which  the  legs  simultaneously  assume  while  both  are  on  the  ground ;  the 
second  group  (fi),  8  to  11,  shows  the  various  positions  of  both  legs  at  the 
time  when  the  posterior  leg  is  elevated  from  the  ground,  but  behind  the 
supported  one;  the  third  group  (6*),  12  to  14,  shows  the  positions  which 
the  legs  assume  when  the  swinging  leg  overtakes  the  standing  one;  and 
the  fourth  group  (/>),  1  to  8,  the  positions  during  the  time  when  the  swing- 
ing leg  is  propelled  in  advance  of  the  resting  one.  The  letters  a,  &,  and  o 
indicate  the  angles  formed  by  the  bones  of  the  right  leg  when  engaged  in 
making  a  step.  The  letters  m,  n,  and  o,  the  positions  assumed  by  the  right 
foot  when  the  trunk  is  rolling  over  it.  g  Shows  the  rotating  forward  of  the 
trunk  upon  the  left  foot  (/)  as  an  axis,  h  Shows  the  rotating  forward  of 
the  left  leg  and  foot  upon  the  trunk  (a)  as  an  axis.  Compare  with  fig.  4, 
p.  21 ;  with  fig.  24,  p.  47 ;  and  with  fig.  20,  p.  55. — After  Weber. 

arms  intersect   at  every  step,  as  shown  at  fig.    19,  p.   39. 
Similar  curves  are  formed  by  the  quadruped  when  walking 


60  ANIMAL  LOCOMOTION. 

(fig.  18,  p.  37),  the  fish  when  swimming  (fig.  32,  p.  68),  and 
the  bird  when  flying  (figs.  73  and  81,  pp.  144  and  157). 

The  alternate  rotation  of  the  trunk  upon  the  limb  and  the 
limb  upon  the  trunk  is  well  seen  in  fig.  27,  p.  59. 

At  A  of  fig.  27  the  trunk  (g)  is  observed  rotating  on  the 
left  foot  (/).  At  D  of  fig.  the  left  leg  (h]  is  seen  rotating  on 
the  trunk  (a,  f) :  these,  as  explained,  are  complementary  move- 
ments. At  A  of  fig.  the  right  foot  (c)  is  firmly  placed  on  the 
ground,  the  left  foot  (/)  being  in  the  act  of  leaving  it.  The 
right  side  of  the  trunk  is  on  a  lower  level  than  the  left,  which 
is  being  elevated,  and  in  the  act  of  rolling  over  the  foot.  At 
B  of  fig.  the  right  foot  (m)  is  still  upon  the  ground,  but  the 
left  foot  having  left  it  is  in  the  act  of  swinging  forward.  At 
C  of  fig.  the  heel  of  the  right  foot  (n)  is  raised  from  the 
ground,  and  the  left  foot  is  in  the  act  of  passing  the  right. 
The  right  side  of  the  trunk  is  now  being  elevated.  At  D  of 
fig.  the  heel  of  the  right  foot  (6)  is  elevated  as  far  as  it  can 
be,  the  toes  of  the  left  foot  being  depressed  and  ready  to 
touch  the  ground.  The  right  side  of  the  trunk  has  now 
reached  its  highest  level,  and  is  in  the  act  of  rolling  over  the 
right  foot.  The  left  side  of  the  trunk,  on  the  contrary,  is 
subsiding,  and  the  left  leg  is  swinging  before  the  right  one, 
preparatory  to  being  deposited  on  the  ground. 

From  the  foregoing  it  will  be  evident  that  the  trunk  and 
limbs  have  pendulum  movements  which  are  natural  and 
peculiar  to  them,  the  extent  of  which  depends  upon  the 
length  of  the  parts.  A  tall  man  and  a  short  man  can  con- 
sequently never  walk  in  step  if  both  walk  naturally  and 
according  to  inclination.1 

In  traversing  a  given  distance  in  a  given  time,  a  tall  man 

1  "  The  number  of  steps  which  a  person  can  take  in  a  given  time  in  walking 
depends,  first,  on  the  length  of  the  leg,  which,  governed  by  the  laws  of  the 
pendulum,  swings  from  behind  forwards ;  secondly,  on  the  earlier  or  later  in- 
terruption which  the  leg  experiences  in  its  arc  of  oscillation  by  being  placed 
on  the  ground.  The  weight  of  the  swinging  leg  and  the  velocity  of  the  trunk 
serve  to  give  the  impulse  by  which  the  foot  attains  a  position  vertical  to  the 
head  of  the  thigh-bone  ;  but  as  the  latter,  according  to  the  laws  of  the  pendu- 
lum, requires  in  tho  quickest  walking  a  given  time  to  attain  that  position, 
or  half  its  entire  curve  of  oscillation,  it  follows  that  every  person  has  a 
certain  measure  for  his  steps,  and  a  certain  number  of  steps  in  a  given 
time,  which,  in  his  natu^il  gait  in  walking,  he  cannot  exceed." 


PROGRESSION  ON  THE  LAND.  Gl 

will  take  fewer  steps  than  a  short  man,  in  the  same  way  that 
a  large  wheel  will  make  fewer  revolutions  in  travelling  over 
a  given  space  than  a  smaller  one.  The  relation  is  a  purely 
mechanical  one.  The  nave  of  the  large  wheel  corresponds  to 
the  ilio-femoral  articulation  (hip-joint)  of  the  tall  man,  the 
spokes  to  his  legs,  and  portions  of  the  rim  to  his  feet.  The 
nave,  spokes,  and  rim  of  the  small  wheel  have  the  same  rela- 
tion to  the  ilio-femoral  articulation  (hip-joint),  legs  and  feet 
of  the  small  man.  When  a  tall  and  short  man  walk  together, 
if  they  keep  step,  and  traverse  the  same  distance  in  the  same 
time,  either  the  tall  man  must  shorten  and  slow  his  steps,  or 
the  short  man  must  lengthen  and  quicken  his. 

The  slouching  walk  of  the  shepherd  is  more  natural  than 
that  of  the  trained  soldier.  It  can  be  kept  up  longer,  and 
admits  of  greater  speed.  In  the  natural  walk,  as  seen  in 
rustics,  the  complementary  movements  are  all  evoked.  In  the 
artificial  walk  of  the  trained  army  man,  the  complementary 
movements  are  to  a  great  extent  suppressed.  Art  is  conse- 
quently not  an  improvement  on  nature  in  the  matter  of  walk- 
ing. In  walking,  the  centre  of  gravity  is  being  constantly 
changed, — a  circumstance  due  to  the  different  attitudes  assumed 
by  the  different  portions  of  the  trunk  and  limbs  at  different 
periods  of  time.  All  parts  of  the  trunk  and  limbs  of  a  biped, 
and  the  same  may  be  said  of  a  quadruped,  move  when  a 
change  of  locality  is  effected.  The  trunk  of  the  biped  and 
quadruped  when  walking  are  therefore  in  a  similar  condition 
to  that  of  the  body  of  the  fish  when  swimming. 

In  running,  all  the  movements  described  are  exaggerated. 
Thus  the  steps  are  more  rapid  and  the  strides  greater.  In 
walking,  a  well-proportioned  six-feet  man  can  nearly  cover 
his  own  height  in  two  steps.  In  running,  he  can  cover  with- 
out difficulty  a  third  more. 

In  fig.  28  (p.  62),  an  athlete  is  represented  as  bending 
forward  prior  to  running. 

The  left  leg  and  trunk,  it  will  be  observed,  are  advanced 
beyond  the  vertical  line  (x),  and  the  arms  are  tucked  up  like 
the  rudimentary  wings  of  the  ostrich,  to  correct  undue  oscilla- 
tion at  the  shoulders,  -occasioned  by  the  violent  oscillation 
produced  at  the  pelvis  in  the  act  of  running. 


G2 


ANIMAL  LOCOMOTION. 


In  order  to  enable  the  right  leg  to  swing  forward,  it  is 
evident  that  it  must  be  flexed,  and  that  the  left  leg  must  be 
extended,  and  the  trunk  raised.  The  raising  of  the  trunk 
causes  it  to  assume  a  more  vertical  position,  and  this  prevents 
the  swinging  leg  from  going  too  far  forwards ;  the  swinging 


Fio.  28. — Preparing  to  run,  from  a  design  by  Flaxman.  Adapted.  In  the  ori- 
ginal of  this  figure  the  right  arm  is  depending  and  placed  on  the  right 
thigh. 

leg  tending  to  oscillate  in  a  slightly  backward  direction  as 
the  trunk  is  elevated.  The  body  is  more  inclined  forwards 
in  running  than  in  walking,  and  there  is  a  period  when  both 
legs  are  off  the  ground,  no  such  period  occurring  in  walking. 
"  In  quick  walking,  the  propelling  leg  acts  more  obliquely  on 
the  trunk,  which  is  more  inclined,  and  forced  forwards  more 
rapidly  than  in  slow  walking.  The  time  when  both  legs  are 
on  the  ground  diminishes  as  the  velocity  increases,  and  it 
vanishes  altogether  when  the  velocity  is  at  a  maximum.  In 
quick  running  the  length  of  step  rapidly  increases,  whilst  the 
duration  slowly  diminishes ;  but  in  slow  running  the  length 
diminishes  rapidly,  whilst  the  time  remains  nearly  the  same. 
The  time  of  a  step  in  quick  running,  compared  to  that  in 
quick  walking,  is  nearly  as  two  to  three,  whilst  the  length  of 
the  steps  are  as  two  to  one ;  consequently  a  person  can  run  in 


PKOGRESSION  ON  THE  LAND.  63 

a  given  time  three  times  as  fast  as  he  can  walk.  In  running, 
the  object  is  to  acquire  a  greater  velocity  in  progression  than 
can  be  attained  in  walking.  In  order  to  accomplish  this, 
instead  of  the  body  being  supported  on  each  leg  alternately, 
the  action  is  divided  into  two  periods,  during  one  of  which 
the  body  is  supported  on  one  leg,  and  during  the  other  it  is 
not  supported  at  all. 

The  velocity  in  running  is  usually  at  the  rate  of  about  ten 
miles  an  hour,  but  there  are  many  persons  who,  for  a  limited 
period,  can  exceed  this  velocity." l 

1  Cyc.  of  Anat.  and  Phy.,  article  "  Motion." 


PROGRESSION  ON  AND  IN  THE  WATER. 


IF  we  direct  our  attention  to  the  water,  we  encounter  a 
medium  less  dense  than  the  earth,  and  considerably  more 
dense  than  the  air.  As  this  element,  in  virtue  of  its  fluidity, 
yields  readily  to  external  pressure,  it  follows  that  a  certain 
relation  exists  between  it  and  the  shape,  size,  and  weight  of 
the  animal  progressing  along  or  through  it.  Those  animals 
make  the  greatest  headway  which  are  of  the  same  specific 
gravity,  or  are  a  little  heavier,  and  furnished  with  extensive 
surfaces,  which,  by  a  dexterous  tilting  or  twisting  (for  the  one 
implies  the  other),  or  by  a  sudden  contraction  and  expansion, 
they  apply  wholly  or  in  part  to  obtain  the  maximum  of  re- 
sistance in  the  one  direction,  and  the  minimum  of  displace- 
ment in  the  other.  The  change  of  shape,  and  the  peculiar 
movements  of  the  swimming  surfaces,  are  rendered  necessary 
by  the  fact,  first  pointed  out  by  Sir  Isaac  Newton,  that  bodies 
or  animals  moving  in  water  and  likewise  in  air  experience  a 
sensible  resistance,  which  is  greater  or  less  in  proportion  to 
the  density  and  tenacity  of  the  fluid  and  the  figure,  superficies, 
and  velocity  of  the  animal. 

To  obtain  the  degree  of  resistance  and  non-resistance  neces- 
sary for  progression  in  water,  Nature,  never  at  fault,  has 
devised  some  highly  ingenious  expedients, — the  Syringograde 
animals  advancing  by  alternately  sucking  up  and  ejecting  the 
water  in  which  they  are  immersed — the  Medusae  by  a  rhyth- 
mical contraction  and  dilatation  of  their  mushroom-shaped 
disk — the  Rotifera  or  wheel-animalcules  by  a  vibratile  action 
of  their  cilia,  which,  according  to  the  late  Professor  Quekett, 
twist  upon  their  pedicles  so  as  alternately  to  increase  and 
diminish  the  extent  of  surface  presented  to  the  water,  as 


PROGRESSION  ON  AND  IN  THE  WATER.  65 

happens  in  the  feathering  of  an  oar.  A  very  similar  plan  is 
adopted  by  the  Pteropoda,  found  in  countless  multitudes  in 
the  northern  seas,  which,  according  to  Eschricht,  use  the 
wing-like  structures  situated  near  the  head  after  the  manner 
of  a  double  paddle,  resembling  in  its  general  features  that  at 
present  in  use  among  the  Greenlanders.  The  characteristic 
movement,  however,  and  that  adopted  in  by  far  the  greater 
number  of  instances,  is  that  commonly  seen  in  the  fish  (figs. 
29  and  30). 


Fio.  30.— The  Salmon  (SaJmn  salar)  swimming  leisurely.  The  body,  it  will  be 
observed,  is  bout  in  two  curves,  one  occurring  towards  the  head,  the  other 
towards  the  tail.  The  shape  of  the  salmon  is  admirably  adapted  for  cleav- 
ing the  water. — Original. 

This,  my  readers  are  aware,  consists  of  a  lashing,  curvi- 
linear, or  flail-like  movement  of  the  broadly  expanded  tail,  which 
oscillates  from  side  to  side  of  the  body,  in  some  instances  with 
immense  speed  and  power.  The  muscles  in  the  fish,  as  has 


66  ANIMAL  LOCOMOTION. 

been  explained,  are  for  this  purpose  arranged  along  the  spinal 
column,  and  constitute  the  bulk  of  the  animal,  it  being  a  law 
that  when  the  extremities  are  wanting,  as  in  the  water-snake, 
or  rudimentary,  as  in  the  fish,  lepidosiren,1  proteus,  and 
axolotl,  the  muscles  of  the  trunk  are  largely  developed.  In 
such  cases  the  onus  of  locomotion  falls  chiefly,  if  not  entirely, 
upon  the  tail  and  lower  portion  of  the  body.  The  operation 
of  this  law  is  well  seen  in  the  metamorphosis  of  the  tad- 
pole, the  muscles  of  the  trunk  and  tail  becoming  modified, 
and  the  tail  itself  disappearing  as  fhe  limbs  of  the  perfect 
frog  are  developed.  The  same  law  prevails  in  certain  instances 
where  the  anterior  extremities  are  comparatively  perfect, 
but  too  small  for  swimming  purposes,  as  in  the  Avhale, 
porpoise,  dugong,  and  manatee,  and  where  both  anterior 
and  posterior  extremities  are  present  but  dwarfed,  as  in  the 
crocodile,  triton,  and  salamander.  The  whale,  porpoise, 
dugong,  and  manatee  employ  their  anterior  extremities  in 
balancing  and  turning,  the  great  organ  of  locomotion  being 
the  tail.  The  same  may  be  said  of  the  crocodile,  triton,  and 
salamander,  all  of  which  use  their  extremities  in  quite  a  sub- 
ordinate capacity  as  compared  with  the  tail.  The  peculiar 
movements  of  the  trunk  and  tail  evoked  in  swimming  are 
seen  to  most  advantage  in  the  fish,  and  may  now  be  briefly 
described. 

Swimming  of  the  Fish,  JVTiale,  Porpoise,  etc. — According  to 
Borelli,2  and  all  who  have  written  since  his  time,  the  fish  in 
swimming  causes  its  tail  to  vibrate  on  either  side  of  a  given 
line,  very  much  as  a  rudder  may  be  made  to  oscillate  by 
moving  its  tiller.  The  line  referred  to  corresponds  to  the 
axis  of  the  fish  when  it  is  at  rest  and  when  its  body  is  straight, 
and  to  the  path  pursued  by  the  fish  when  it  is  swimming. 
It  consequently  represents  the  axis  of  the  fish  and  the  axis  of 

1  The  lepidosiren  is  furnished  with  two  tapering  flexible  stem-like  bodies, 
which  depend  from  the  anterior  ventral  aspect  of  the  animal,  the  siren  having 
in  the  same  region  two  pairs  of  rudimentary  limbs  furnished  with  four  imper- 
fect toes,  while  the  proteus  has  anterior  extremities  armed  with  three  toes 
each,  and  a  very  feeble  posterior  extremity  terminating  in  two  toes. 

8  Borelli,  "  De  motu  Animalium,"  plate  4,  fig.  5  sm.  4to,  2  vols.  Romse, 
1680. 


PROGRESSION  ON  AND  IN  THE  WATER.  67 

motion.  According  to  this  theory  the  tail,  when  flexed  or 
carved  to  make  what  is  termed  the  back  or  non-effective 
stroke,  is  forced  away  from  the  imaginary  line,  its  curved, 
concave,  or  biting  surface  being  directed  outwards.  When, 
on  the  other  hand,  the  tail  is  extended  to  make  what  is  termed 
the  effective  or  forward  stroke,  it  is  urged  towards  the  ima- 
ginary line,  its  convex  or  non-biting  surface  being  directed 
inwards  (fig.  31). 


Z 

Fia.  31.— Swimming  of  the  Fish.— (After  Borelli.) 

When  the  tail  strikes  in  the  direction  a  i,  the  head  of  the 
fish  is  said  to  travel  in  the  direction  c  h.  When  the  tail 
strikes  in  the  direction  g  e,  the  head  is  said  to  travel  in  the 
direction  c  b;  these  movements,  when  the  tail  is  urged  with 
sufficient  velocity,  causing  the  body  of  the  fish  to  move  in 
the  line  d  c  f.  The  explanation  is  apparently  a  satisfactory 
one ;  but  a  careful  analysis  of  the  swimming  of  the  living  fish 
induces  me  to  believe  it  is  incorrect.  According  to  this,  the 
commonly  received  view,  the  tail  would  experience  a  greater 
degree  of  resistance  during  the  back  stroke,  i.e.  when  it  is 
flexed  and  carried  away  from  the  axis  of  motion  (d  c  f)  than 
it  would  during  the  forward  stroke,  or  when  it  is  extended 
and  carried  towards  the  axis  of  motion.  This  follows,  because 
the  concave  surface  of  the  tail  is  applied  to  the  water  during 
what  is  termed  the  back  or  non-effective  stroke,  and  the  con- 
vex surface  during  what  is  termed  the  forward  or  effective 
stroke.  This  is  just  the  opposite  of  what  actually  happens, 
and  led  Sir  John  Lubbock  to  declare  that  there  was  a  period 
in  which  the  action  of  the  tail  dragged  the  fish  backwards, 
which,  of  course,  is  erroneous.  There  is  this  further  difficulty. 
When  the  tail  of  the  fish  is  urged  in  the  direction  g  e,  the 


C8  ANIMAL  LOCOMOTION. 

head  does  not  move  in  the  direction  c  b  as  stated,  but  in  the 
direction  c  h,  the  body  of  the  fish  describing  the  arc  of  a 
circle,  a  c  h.  This  is  a  matter  of  observation.  If  a  fish  when 
resting  suddenly  forces  its  tail  to  one  side  and  curves  its 
body,  the  fish  describes  a  curve  in  the  water  corresponding 
to  that  described  by  the  body.  If  the  concavity  of  the 
curve  formed  by  the  body  is  directed  to  the  right  side, 
the  fish  swims  in  a  curve  towards  that  side.  To  this  there 
is  no  exception,  as  any  one  may  readily  satisfy  himself,  by 
watching  the  movements  of  gold  fish  in  a  vase.  Observation 
and  experiment  have  convinced  me  that  when  a  fish  swims  it 
never  throws  its  body  into  a  single  curve,  as  represented  at 
fig.  31,  p.  67,  but  always  into  a  double  or  figure-of-8  curve,  as 
shown  at  fig.  32.1 


FIG.  32.—  Swimming  of  the  Sturgeon.  From  Nature.  Compare  with  figs.  IS 
and  19,  pp.  37  and  39 ;  fig.  23,  p.  43 ;  and  figs.  64  to  73,  pp.  139,  141  aud 
-144.—  Original. 

The  double  curve  is  necessary  to  enable  the  fish  to  present 
a  convex  or  non-biting  surface  (c)  to  the  water  during  flexion 
(the  back  stroke  of  authors),  when  the  tail  is  being  forced 
away  from  the  axis  of  motion  (a  b),  and  a  concave  or  biting 
surface  (s)  during  extension  (the  forward  or  effective  stroke  of 
authors),  when  the  tail  is  being  forced  with  increased  energy 
towards  the  axis  of  motion  (a  b) ;  the  resistance  occasioned  by 
a  concave  surface,  when  compared  with  a  convex  one,  being  in 
the  ratio  of  two  to  one.  The  double  or  complementary  curve 
into  which  the  fish  forces  its  body  when  swimming,  is  neces- 
sary to  correct  the  tendency  which  the  head  of  the  fish  has 
to  move  in  the  same  direction,  or  to  the  same  side  as  that 

1  It  is  only  when  a  fish  is  turning  that  it  forces  its  body  into  a  single  curve. 


PKOGKESSION  ON  AND  IN  THE  WATER.  60 

towards  which  the  tail  curves.  In  swimming,  the  body  of 
the  fish  describes  a  waved  track,  but  this  can  only  be  done 
when  the  head  and  tail  travel  in  opposite  directions,  and  on 
opposite  sides  of  a  given  line,  as  represented  at  fig.  32. 
The  anterior  and  posterior  portions  of  the  fish  alternately 
occupy  the  positions  indicated  at  d  c  and  w  v;  the  fish  oscil- 
lating on  either  side  of  a  given  line,  and  gliding  along  by  a 
sinuous  or  wave  movement. 

I  have  represented  the  body  of  the  fish  as  forced  into  two 
curves  when  swimming,  as  there  are  never  less  than  two. 
These  I  designate  the  cephalic  (d)  and  caudal  (c)  curves,  from 
their  respective  positions.  In  the  long-bodied  fishes,  such  as  the 
eels,  the  number  of  the  curves  is  increased,  but  in  every  case 
the  curves  occur  in  pairs,  and  are  complementary.  The  cephalic 
and  caudal  curves  not  only  complement  each  other,  but  they  act 
as  fulcra  for  each  other,  the  cephalic  curve,  with  the  water  seized 
by  it,  forming  the  point  d'appui  for  the  caudal  one,  and  vice  versd. 
The  fish  in  swimming  lashes  its  tail  from  side  to  side,  precisely 
as  an  oar  is  lashed  from  side  to  side  in  sculling.  It  therefore 
describes  a  figure-of-8  track  in  the  water  (efghijkl  of 
fig.  32).  During  each  sweep  or  lateral  movement  the  tail  is 
both  extended  and  flexed.  It  is  extended  and  its  curve 
reduced  when  it  approaches  the  line  ab  of  fig.  32,  and  flexed, 
and  a  new  curve  formed,  when  it  recedes  from  the  line  in 
question.  The  tail  is  effective  as  a  propeller  both  during 
flexion  and  extension,  so  that,  strictly  speaking,  the  tail  has 
no  back  or  non-effective  stroke.  The  terms  effective  and 
non-effective  employed  by  authors  are  applicable  only  in  a 
comparative  and  restricted  sense;  the  tail  always  operating, 
but  being  a  less  effective  propeller,  when  in  the  act  of  being 
flexed  or  curved,  than  when  in  the  act  of  being  extended  or 
straightened.  By  always  directing  the  concavity  of  the  tail 
(s  and  t)  towards  the  axis  of  motion  (a  b)  during  extension, 
and  its  convexity  (c  and  v)  away  from  the  axis  of  motion  (a  b) 
during  flexion,  the  fish  exerts  a  maximum  of  propelling  power 
with  a  minimum  of  slip.  In  extension  of  the  tail  the  caudal 
curve  (s)  is  reduced  as  the  tail  travels  towards  the  line  a  b. 
In  flexion  a  new  curve  (v)  is  formed  as  the  tail  travels  from 
the  line  a  b.  While  the  tail  travels  from  s  in  the  direction  /, 


70  ANIMAL  LOCOMOTION. 

the  head  travels  from  d  in  the  direction  w.  There  is  there- 
fore a  period,  momentary  it  must  be,  when  both  the  cephalic 
and  caudal  curves  are  reduced,  and  the  body  of  the  fish  is 
straight,  and  free  to  advance  without  impediment.  The 
different  degrees  of  resistance  experienced  by  the  tail  in  de- 
scribing its  figure-of-8  movements,  are  represented  by  the 
different-sized  curves  ef,  g  h,  ij,  and  k  I  of  fig.  32,  p.  68.  The 
curves  ef  indicate  the  resistance  experienced  by  the  tail 
during  flexion,  when  it  is  being  carried  away  from  and  to  the 
right  of  the  line  a  b.  The  curves  g  h  indicate  the  resistance 
experienced  by  the  tail  when  it  is  extended  and  carried  towards 
the  line  a  b.  This  constitutes  a  half  vibration  or  oscillation  of 
the  tail.  The  curves  i  j  indicate  the  resistance  experienced 
by  the  tail  when  it  is  a  second  time  flexed  and  carried  away 
from  and  to  the  left  of  the  line  a  b.  The  curves  Jc  I  indicate 
the  resistance  experienced  by  the  tail  when  it  is  a  second 
time  extended  and  carried  towards  the  line  a  b.  This  consti- 
tutes a  complete  vibration.  These  movements  are  repeated 
in  rapid  succession  so  long  as  the  fish  continues  to  swim 
forwards.  They  are  only  varied  when  the  fish  wishes  to  turn 
round,  in  which  case  the  tail  gives  single  strokes  either  to 
the  right  or  left,  according  as  it  wishes  to  go  to  the  right  or 
left  side  respectively.  The  resistance  experienced  by  the  tail 
when  in  the  positions  indicated  by  ef  and  ij  is  diminished 
by  the  tail  being  slightly  compressed,  by  its  being  moved 
more  slowly,  and  by  the  fish  rotating  on  its  long  axis  so  as 
to  present  the  tail  obliquely  to  the  water.  The  resistance 
experienced  by  the  tail  when  in  the  positions  indicated  by 
g  h,  k  I,  is  increased  by  the  tail  being  divaricated,  by  its  being 
moved  with  increased  energy,  and  by  the  fish  re-rotating  on 
its  long  axis,  so  as  to  present  the  flat  of  the  tail  to  the  water. 
The  movements  of  the  tail  are  slowed  when  the  tail  is  carried 
away  from  the  line  a  b,  and  quickened  when  the  tail  is  forced 
towards  it.  Nor  is  this  all.  When  the  tail  is  moved  slowly 
away  from  the  line  a  b,  it  draws  a  current  after  it  which, 
being  met  by  the  tail  when  it  is  urged  with  increased  velocity 
towards  the  line  a  b,  enormously  increases  the  hold  which  the 
tail  takes  of  the  water,  and  consequently  its  propelling  power. 
The  tail  may  be  said  to  work  without  slip,  and  to  produce 


PROGRESSION  ON  AND  IN  THE  WATER.  71 

the  precise  kind  of  currents  which  afford  it  the  greatest 
leverage.  In  this  respect  the  tail  of  the  fish  is  infinitely 
superior  as  a  propelling  organ  to  any  form  of  screw  yet  de- 
vised. The  screw  at  present  employed  in  navigation  ceases  to 
be  effective  when  propelled  beyond  a  given  speed.  The 
screw  formed  by  the  tail  of  the  fish,  in  virtue  of  its  recipro- 
cating action,  and  the  manner  in  which  it  alternately  eludes 
and  seizes  the  water,  becomes  more  effective  in  proportion  to 
the  rapidity  with  which  it  is  made  to  vibrate.  The  remarks 
now  made  of  the  tail  and  the  water  are  equally  apropos  of  the 
wing  and  the  air.  The  tail  and  the  wing  act  on  a  common 
principle.  A  certain  analogy  may  therefore  be  traced  be- 
tween the  water  and  air  as  media,  and  between  the  tail  and 
extremities  as  instruments  of  locomotion.  From  this  it  fol- 
lows that  the  water  and  air  are  acted  upon  by  curves  or  wave- 
pressure  emanating  in  the  one  instance  from  the  tail  of  the 
fish,  and  in  the  other  from  the  wing  of  the  bird,  the  recipro- 
cating and  opposite  curves  into  which  the  tail  and  wing  are 
thrown  in  swimming  and  flying  constituting  mobile  helices 
or  screws,  which,  during  their  action,  produce  the  precise 
kind  and  degree  of  pressure  adapted  to  fluid  media,  and 
to  which  they  respond  with  the  greatest  readiness.  The 
whole  body  of  the  fish  is  thrown  into  action  in  swimming ; 
but  as  the  tail  and  lower  half  of  the  trunk  are  more  free  to 
move  than  the  head  and  upper  half,  which  are  more  rigid, 
and  because  the  tendons  of  many  of  the  trunk-muscles  are 
inserted  into  the  tail,  the  oscillation  is  greatest  in  the  direction 
of  the  latter.  The  muscular  movements  travel  in  spiral  waves 
from  before  backwards ;  and  the  waves  of  force  react  upon  the 
water,  and  cause  the  fish  to  glide  forwards  in  a  series  of  curves. 
Since  the  head  and  tail,  as  has  been  stated,  always  travel  in 
opposite  directions,  and  the  fish  is  constantly  alternating  or 
changing  sides,  it  in  reality  describes  a  waved  track.  These 
remarks  may  be  readily  verified  by  a  reference  to  the  swim- 
ming of  the  sturgeon,  whose  movements  are  unusually  deli- 
berate and  slow.  The  number  of  curves  into  which  the  body 
of  the  fish  is  thrown  in  swimming  is  increased  in  the  long- 
bodied  fishes,  as  the  eels,  and  decreased  in  those  whose  bodies 
are  short  or  are  comparatively  devoid  of  flexibility.  In  pro- 


72  ANIMAL  LOCOMOTION. 

portion  as  the  curves  into  which  the  body  is  thrown  in  swim- 
ming are  diminished,  the  degree  of  rotation  at  the  tail  or  in 
the  fins  is  augmented,  some  fishes,  as  the  mackerel,  using  the 
tail  very  much  after  the  manner  of  a  screw  in  a  steam-ship. 
The  fish  may  thus  be  said  to  drill  the  water  in  two  directions, 
viz.  from  behind  forwards  by  a  twisting  or  screwing  of  the 
body  on  its  long  axis,  and  from  side  to  side  by  causing  its 
anterior  and  posterior  portions  to  assume  opposite  curves. 
The  pectoral  and  other  fins  are  also  thrown  into  curves  when 
in  action,  the  movement,  as  in  the  body  itself,  travelling  in 
spiral  waves ;  and  it  is  worthy  of  remark  that  the  wing  of 
the  insect,  bat,  and  bird  obeys  similar  impulses,  the  pinion,  as 
I  shall  show  presently,  being  essentially  a  spiral  organ. 

The  twisting  of  the  pectoral  fins  is  well  seen  in  the  com- 
mon perch  (Perca  fluviatilis),  and  still  better  in  the  15-spined 
Stickleback  (Gasterosteus  spinosus),  which  latter  frequently 
pi  ogresses  by  their  aid.  alone.1  In  the  stickleback,  the  pec- 
toral fins  are  so  delicate,  and  are  plied  Avith  such  vigour,  that 
the  eye  is  apt  to  overlook  them,  particularly  when  in  motion. 
The  action  of  the  fins  can  be  reversed  at  pleasure,  so  that  it 
is  by  no  means  an  unusual  thing  to  see  the  stickleback  pro- 
gressing tail  first.  The  fins  are  rotated  or  twisted,  and  their 
free  margins  lashed  about  by  spiral  movements  which  closely 
resemble  those  by  which  the  wings  of  insects  are  propelled.2 
The  rotating  of  the  fish  upon  its  long  axis  is  seen  to  advan- 
tage in  the  shark  and  sturgeon,  the  former  of  which  requires 
to  turn  on  its  side  before  it  can  seize  its  prey, — and  likewise 

1  The  Sywgnathi,  or  Pipefishes,  swim  chiefly  by  the  undulating  movement 
of  the  dorsal  fin. 

*  If  the  pectoral  fins  are  to  be  regarded  as  the  homologues  of  the  anterior 
extremities  (which  they  unquestionably  are),  it  is  not  surprising  that  in  them 
the  spiral  rotatory  movements  which  are  traceable  in  the  extremities  of 
quadrupeds,  and  so  fully  developed  in  the  wings  of  bats  and  birds,  should 
be  clearly  foreshadowed.  "  The  muscles  of  the  pectoral  fins,"  remarks  Pro- 
fessor Owen,  "  though,  when  compared  with  those  of  the  homologous  mem- 
bers in  higher  vertebrates,  they  are  very  small,  few,  and  simple,  yet  suffice 
for  all  the  requisite  movements  of  the  fins — elevating,  depressing,  advancing, 
and  again  laying  them  prone  and  flat,  by  an  oblique  stroke,  upon  the  sides  of 
the  body.  The  rays  or  digits  of  both  pectorals  and  ventrals  (the  homologues 
of  the  posterior  extremities)  can  be  divaricated  and  approximated,  and  the 
intervening  webs  .spread  out  or  folded  up." — Op.  cit.  vol.  i  p.  252. 


PROGRESSION  ON  AND  IN  THE  WATEK. 


73 


in  the  pipefish,  Avhose  motions  are  unwontedly  sluggish. 
The  twisting  of  the  tail  is  occasionally  well  marked  in  the 
swimming  of  the  salamander.  In  those  remarkable  mammals, 
the  whale,1  porpoise,  manatee,  and  dugong  (figs.  33,  34,  and 
35),  the  movements  are  strictly  analogous  to  those  of  the  fish, 


-s.,      " 


FIG.  33.— The  Porpoise  (Phocmna  cornmunis).  Here  the  tail  is  principally  en- 
gaged in  swimming,  the  anterior  extremities  being  rudimentary,  ami  resem- 
bling the  pectoral  fins  of  lishes.  Compare  with  iig.  30,  p.  05.  —  Original. 


FIG.  34. — The  Manatee  'Manatiis  American-its}.  In  this  the  anterior  extremities 
are  more  developed  than  in  the  porpoise,  lint  still  the  tail  is  the  great  orgiin 
of  natation.  Compare  with  fig.  33,  p.  73,  and  with  Iig.  30,  p.  C5.  The  shape 
of  the  manatee  and  porpoise  is  essentially  that  of  the  fish.  —  Original. 

the  only  difference  being  that  the  tail  acts  from  above  down- 
wards or  vertically,  instead  of  from  side  to  side  or  laterally. 
The  anterior  extremities,  which  in  those  animals  are  com- 
paratively perfect,  are  rotated  on  their  long  axes,  and  applied 
obliquely  and  non-obliquely  to  the  water,  to  assist  in  balanc- 
ing and  turning.  Natation  is  performed  almost  exclusively  by 
the  tail  and  lower  half  of  the  trunk,  the  tail  of  the  whale 
exerting  prodigious  power. 

It  is  otherwise  with  the  Rays,  where  the  hands  are  princi- 

1   Viile  "  Remarks  on  the  Swimming  of  the  Cetaceans,"  by  Dr.    Murie, 
Proc.  Zool.  Soc.,  1865,  pp.  209,  210. 


74 


ANIMAL  LOCOMOTION. 


pally  concerned  in  progression,  these  flapping  about  in  the 
water  very  much  as  the  wings  of  a  bird  flap  about  in  the  air. 
In  the  beaver,  the  tail  is  flattened  from  above  downwards,  as 
in  the  foregoing  mammals,  but  in  swimming  it  is  made  to 


Fio.  85.— Skeleton  of  the  Dugong.  In  this  curious  mammal  the  anterior 
extremities  are  more  developed  than  in  the  manatee  and  porpoise,  and 
resemble  those  found  in  the  seal,  sea-hear,  and  walrus.  They  are  useful 
in  balancing  and  turning,  the  tail  being  the  effective  instrument  of  propul- 
sion. The  vertebral  column  closely  resembles  that  of  the  fish,  and  allows 
the  tail  to  be  lashed  freely  about  in  a  vertical  direction.  Compare  with 
Jig.  29,  p.  65.— (After  Dallas.) 

act  upon  the  water  laterally  as  in  the  fish.  The  tail  of  the 
bird,  which  is  also  compressed  from  above  downwards,  can 
be  twisted  obliquely,  and  when  in  this  position  may  be  made 
to  perform,  the  office  of  a  rudder. 

Swimming  of  ihe,  Seal,  Sea-Bear,  and  Walrus. — In  the  seal, 
the  anterior  and  posterior  extremities  are  more  perfect  than 
in  the  whale,  porpoise,  dugoiig,  and  manatee;  the  general 


Fio.  36  —The  Seal  (Phocafaetida,  Mull.),  adapted  principally  for  water.  The 
extremities  are  larger  than  in  the  porpoise  and  manatee.  Compare  with 
figs.  33  and  34,  p.  73.—  Original. 

form,  however,  and  mode  of  progression  (if  the  fact  of  its 
occasionally  swimming  on  its  back  be  taken  into  account),  is 
essentially  fish-like. 


PROGRESSION  ON  AND  IN  THE  WATER.  75 

A  peculiarity  is  met  with  in  the  swimming  of  the  seal,  to 
which  I  think  it  proper  to  direct  attention.  When  the  lower 
portion  of  the  body  and  posterior  extremities  of  these  creatures 
are  flexed  and  tilted,  as  happens  during  the  back  and  least 
effective  stroke,  the  naturally  expanded  feet  are  more  or  less 
completely  closed  or  pressed  together,  in  order  to  diminish 
the  extent  of  surface  presented  to  the  water,  and,  as  a  con- 
sequence, to  reduce  the  resistance  produced.  The  feet  are 
opened  to  the  utmost  during  extension,  when  the  more  effec- 
tive stroke  is  given,  in  which  case  they  present  their  maximum 
of  surface.  They  form  powerful  propellers,  both  during 
flexion  and  extension. 

The  swimming  apparatus  of  the  seal  is  therefore  more 
highly  differentiated  than  that  of  the  whale,  porpoise,  dugong, 
and  manatee ;  the  natatory  tail  in  these  animals  being,  from 
its  peculiar  structure,  incapable  of  lateral  compression.1  It 
would  appear  that  the  swimming  appliances  of  the  seals  (where 
the  feet  open  and  close  as  in  swimming-birds)  are  to  those  of 
the  sea-mammals  generally,  what  the  feathers  of  the  bird's 
wing  (these  also  open  and  close  in  flight)  are  to  the  continuous 
membrane  forming  the  wing  of  the  insect  and  bat. 

The  anterior  extremities  or  flippers  of  the  seal  are  not 
engaged  in  swimming,  but  only  in  balancing  and  in  changing 
position.  When  so  employed  the  fore  feet  open  and  close, 
though  not  to  the  same  extent  as  the  hind  ones ;  the  resist- 
ance and  non-resistance  necessary  being  secured  by  a  partial 
rotation  and  tilting  of  the  flippers.  By  this  twisting  and 
untwisting,  the  narrow  edges  and  broader  portions  of  the 
flippers  are  applied  to  the  water  alternately.  The  rotating 
and  tilting  of  the  anterior  and  posterior  extremities,  and  the 
opening  and  closing  of  the  hands  and  feet  in  the  balancing 
and  swimming  of  the  seal,  form  a  series  of  strictly  progressive 
and  very  graceful  movements.  They  are,  however,  performed 
so  rapidly,  and  glide  into  each  other  so  perfectly,  as  to  render 
an  analysis  of  them  exceedingly  difficult. 

1  In  a  few  instances  the  caudal  fin  of  the  fish,  as  has  been  already  stated, 
is  more  or  less  pressed  together  during  the  Lack  stroke,  the  compression  and 
tilting  or  twisting  of  the  tail  taking  place  synchronously. 


76  ANIMAL  LOCOMOTION. 

In  the  Sea-Bear  (Otaria  jubata)  the  anterior  extremities 
attain  sufficient  magnitude  and  power  to  enable  the  animal  to 
progress  by  their  aid  alone;  the  feet  and  the  lower  portions  of 
the  body  being  moved  only  sufficiently  to  maintain,  correct,  or 
alter  the  course  pursued  (fig.  73).  The  anterior  extremities  are 
flattened  out,  and  greatly  resemble  wings,  particularly  those  of 
the  penguin  and  auk,  which  are  rudimentary  in  character. 
Thus  they  have  a  thick  and  comparatively  stiff  anterior 
margin ;  and  a  thin,  flexible,  and  more  or  less  elastic  posterior 
margin.  They  are  screw  structures,  and  when  elevated  and 
depressed  in  the  water,  twist  and  untwist,  screw-fashion, 
precisely  as  wings  do,  or  the  tails  of  the  fish,  whale,  dugong, 
and  manatee. 


Fio.  37.— The  Sea-Bear  (Otaria  jubala),  adapted  principally  for  swimming 
and  diving.  It  also  walks  with  tolerable  facility.  Its  extremities  are  larger 
than  those  of  the  seal,  and  its  movements,  both  in  and  out  of  the  water 
more  varied. — Original. 

This  remarkable  creature,  which  I  have  repeatedly  watched 
at  the  Zoological  Gardens1  (London),  appears  to  fly  in  the 
water,  the  universal  joints  by  which  the  arms  are  attached  to 
the  shoulders  enabling  it,  by  partially  rotating  and  twisting 

1  The  unusual  opportunities  afforded  by  this  unrivalled  collection  have 
enabled  me  to  determine  with  considerable  accuracy  the  movements  of  the 
various  land-animals,  as  well  as  the  motions  of  the  wings  and  feet  of  birds, 
both  in  and  out  of  the  water.  I  have  also  studied  under  the  most  favour-' 
able  circumstances  the  movements  of  the  otter,  sea-bear,  seal,  walrus,  porpoise, 
turtle,  triton,  crocodile,  frog,  lepidosiren,  proteus,  axolotl,  and  the  severJ 
orders  of  fishes. 


PROGRESSION  ON  AND  IN  THE  WATER.  77 

them,  to  present  the  palms  or  flat  of  the  hands  to  the  water 
the  one  instant,  and  the  edge  or  narrow  parts  the  next.  In 
swimming,  the  anterior  or  thick  margins  of  the  flippers  are 
directed  downwards,  and  similar  remarks  are-  to  be  made  of  the 
anterior  extremities  of  the  walrus,  great  auk,  and  turtle.1 

The  flippers  are  advanced  alternately;  and  the  twisting, 
screw-like  movement  which  they  exhibit  in  action,  and  which 
I  have  carefully  noted  on  several  occasions,  bears  considerable 
resemblance  to  the  motions  witnessed  in  the  pectoral  fins  of 
fishes.  It  may  be  remarked  that  the  twisting  or  spiral  move- 
ments of  the  anterior  extremities  are  calculated  to  utilize  the 
water  to  the  utmost — the  gradual  but  rapid  operation  of  the 
helix  enabling  the  animal  to  lay  hold  of  the  water  and  dis- 
entangle itself  with  astonishing  facility,  and  with  the  mini- 
mum expenditure  of  power.  In  fact,  the  insinuating  motion 
of  the  screw  is  the  only  one  which  can  contend  successfully 
with  the  liquid  element;  and  it  appears  to  me  that  this 
remark  holds  even  more  true  of  the  air.  It  also  applies 
within  certain  limits,  as  has  been  explained,  to  the  land. 
The  otaria  or  sea-bear  swims,  or  rather  flies,  under  the  water 
with  remarkable  address  and  with  apparently  equal  ease  in 
an  upward,  downward,  and  horizontal  direction,  by  muscular 
efforts  alone — an  observation  which  may  likewise  be  made 
regarding  a  great  number  of  fishes,  since  the  swimming- 
bladder  or  float  is  in  many  entirely  absent.2  Compare  with 
figs.  33,  34,  35,  and  36,  pp.  73  and  74.  The  walrus,  a.  living 
specimen  of  which  I  had  an  opportunity  of  frequently  examin- 
ing, is  nearly  allied  to  the  seal  and  sea-bear,  but  differs  from 
both  as  regards  its  manner  of  swimming.  The  natation  of  this 
rare  and  singularly  interesting  animal,  as  I  have  taken  great 
pains  to  satisfy  myself,  is  effected  by  a  mixed  movement — the 
anterior  and  posterior  extremities  participating  in  nearly  an 
equal  degree.  The  anterior  extremities  or  flippers  of  the 
walrus,  morphologically  resemble  those  of  the  seal,  but  physio- 
logically those  of  the  sea-bear ;  while  the  posterior  extremities 

1  This  is  the  reverse  of  what  takes  place  in  flying,  the  anterior  or  thick 
margins  of  the  wings  being  invariably  directed  upicards. 

2  The  air-bladder  is  wanting  in  the  dennopteri,  plagiostomi,  and  pleuronec- 
ticUe. — Owen,  op.  cit.  p.  255. 


78  ANIMAL  LOCOMOTION. 

possess  many  of  the  peculiarities  of  the  hind  legs  of  the  sea- 
bear,  but  display  the  movements  peculiar  to  those  of  the  seal. 
In  other  words,  the  anterior  extremities  or  flippers  of  the 
walrus  are  moved  alternately,  and  reciprocate,  as  in  the  sea- 
bear  ;  whereas  the  posterior  extremities  are  lashed  from  side 
to  side  by  a  twisting,  curvilinear  motion,  precisely  as  in  the 
seal  The  walrus  may  therefore,  as  far  as  the  physiology  of 
its  extremities  is  concerned,  very  properly  be  regarded  as 
holding  an  intermediate  position  between  the  seals  on  the 
one  hand,  and  the  sea-bears  or  sea-lions  on  the  other. 

Swimming  of  Man. — The  swimming  of  man  is  artificial  in 
its  nature,  and  consequently  does  not,  strictly  speaking,  fall 
within  the  scope  of  the  present  work.  I  refer  to  it  princi- 
pally with  a  view  to  showing  that  it  resembles  in  its  general 
features  the  swimming  of  animals. 

The  human  body  is  lighter  than  the  water,  a  fact  of  con- 
siderable practical  importance,  as  showing  that  each  has  in 
himself  that  which  will  prevent  his  being  drowned,  if  he  will 
only  breathe  naturally,  and  desist  from  struggling. 

The  catastrophe  of  drowning  is  usually  referrible  to  nervous 
agitation,  and  to  spasmodic  and  ill- directed  efforts  in  the 
extremities.  All  swimmers  have  a  vivid  recollection  of  the 
great  difficulty  experienced  in  keeping  themselves  afloat,  when 
they  first  resorted  to  aquatic  exercises  and  amusements.  In 
especial  they  remember  the  short,  vigorous,  but  flurried,  mis- 
directed, and  consequently  futile  strokes  which,  instead  of 
enabling  them  to  skim  the  surface,  conducted  them  inevitably 
to  the  bottom.  Indelibly  impressed  too  are  the  ineffectual 
attempts  at  respiration,  the  gasping  and  puffing  and  the  swal- 
lowing of  water,  inadvertently  gulped  instead  of  air. 

In  order  to  swim  well,  the  operator  must  be  perfectly  calm. 
He  must,  moreover,  know  how  to  apply  his  extremities  to  the 
water  with  a  view  to  propulsion.  As  already  stated,  the  body 
will  float  if  left  to  itself;  the  support  obtained  is,  however, 
greatly  increased  by  projecting  it  along  the  surface  of  the 
water.  This,  as  all  swimmers  are  aware,  may  be  proved  by 
experiment.  It  is  the  same  principle  which  prevents  a  thin 
flat  stone  from  sinking  when  projected  with  force  against  the 
surface  of  water.  A  precisely  similar  result  is  obtained  if  the 


PROGRESSION  ON  AND  IN  THE  WATER.  79 

body  be  placed  slantingly  in  a  strong  current,  and  the  hands 
made  to  grasp  a  stone  or  branch.  In  this  case  the  body  is 
raised  to  the  surface  of  the  stream  by  the  action  of  the  run- 
ning water,  the  body  remaining  motionless.  The  quantity  of 
water  which,  under  the  circumstances,  impinges  against  the 
body  in  a  given  time  is  much  greater  than  if  the  body  was 
simply  immersed  in  still  water.  To  increase  the  area  of  sup- 
port, either  the  supporting  medium  or  the  body  supported 
must  move.  The  body  is  supported  in  water  very  much  as 
the  kite  is  supported  in  air.  In  both  cases  the  body  and  the 
kite  are  made  to  strike  the  water  and  the  air  at  a  slight 
upward  angle.  When  the  extremities  are  made  to  move  in 
a  horizontal  or  slightly  downward  direction,  they  at  once 
propel  and  support  the  body.  When,  however,  they  are  made 
to  act  in  an  upward  direction,  as  in  diving,  they  submerge 
the  body.  This  shows  that  the  movements  of  the  swimming 
surfaces  may,  according  to  their  direction,  either  augment  or 
destroy  buoyancy.  The  swimming  surfaces  enable  the  seal, 
sea-bear,  otter,  ornithorhynchus,  bird,  etc.,  to  disappear  from 
and  regain  the  surface  of  the  water.  Similar  remarks  may 
be  made  of  the  whale,  dugong,  manatee,  and  fish. 

Man,  in  order  to  swim,  must  learn  the  art  of  swimming. 
He  must  serve  a  longer  or  shorter  apprenticeship  to  a  new 
form  of  locomotion,  and  acquire  a  new  order  of  movements. 
It  is  otherwise  with  the  majority  of  animals.  Almost  all 
quadrupeds  can  swim  the  first  time  they  are  immersed, 
as  may  readily  be  ascertained  by  throwing  a  newly  born 
kitten  or  puppy  into  the  water.  The  same  may  be  said  of 
the  greater  number  of  birds.  This  is  accounted  for  by  the  fact 
that  quadrupeds  and  birds  are  lighter,  bulk  for  bulk,  than 
water,  but  more  especially,  because  in  walking  and  running 
the  movements  made  by  their  extremities  are  precisely  those 
required  in  swimming.  They  have  nothing  to  learn,  as  it 
were.  They  are  buoyant  naturally,  and  if  they  move  their 
limbs  at  all,  which  they  do  instinctively,  they  swim  of  neces- 
sity. It  is  different  with  man.  The  movements  made  by 
him  in  walking  and  running  are  not  those  made  by  him  in 
swimming ;  neither  is  the  position  resorted  to  in  swimming 
that  which  characterizes  him  on  land.  The  vertical  position 


80  ANIMAL  LOCOMOTION. 

is  not  adapted  for  water,  and,  as  a  consequence,  he  requires 
to  abandon  it  and  assume  a  horizontal  one ;  he  requires,  in 
fact,  to  throw  himself  flat  upon  the  water,  either  upon  his 
side,  or  upon  his  dorsal  or  ventral  aspect.  This  position 
assimilates  him  to  the  quadruped  and  bird,  the  fish,  and 
everything  that  swims ;  the  trunks  of  all  swimming  animals 
being  placed  in  a  prone  position.  Whenever  the  horizontal 
position  is  assumed,  the  swimmer  can  advance  in  any  direc- 
tion he  pleases.  His  extremities  are  quite  free,  and  only 
require  to  be  moved  in  definite  directions  to  produce  definite 
results.  The  body  can  be  propelled  by  the  two  arms,  or  the 
two  legs ;  or  by  the  right  arm  and  leg,  or  the  left  arm  and 
leg ;  or  by  the  right  arm  and  left  leg,  or  the  left  arm  and 
right  leg.  Most  progress  is  made  when  the  two  arms  and 
the  two  legs  are  employed.  An  expert  swimmer  can  do 
whatever  he  chooses  in  water.  Thus  he  can  throw  himself 
upon  his  back,  and  by  extending  his  arms  obliquely  above  his 
head  until  they  are  in  the  same  plane  with  his  body,  can 
float  without  any  exertion  whatever;  or,  maintaining  the 
floating  position,  he  can  fold  his  arms  upon  his  chest  and  by 
alternately  flexing  and  extending  his  lower  extremities,  can 
propel  himself  with  ease  and  at  considerable  speed  ;  or,  keeping 
his  legs  in  the  extended  position  and  motionless,  he  can  pro- 
pel himself  by  keeping  his  arms  close  to  his  body,  and  causing 
his  hands  to  work  like  sculls,  so  as  to  make  figure-of-8  loops 
in  the  water.  This  motion  greatly  resembles  that  made  by 
the  swimming  wings  of  the  penguin.  It  is  most  effective 
when  the  hands  are  turned  slightly  upwards,  and  a  greater  or 
less  backward  thrust  given  each  time  the  hands  reciprocate. 
The  progress  made  at  first  is  slow,  but  latterly  very  rapid, 
the  rapidity  increasing  according  to  the  momentum  acquired. 
The  swimmer,  in  addition  to  the  foregoing  methods,  can 
throw  himself  upon  his  face,  and  by  alternately  flexing  and  ex- 
tending his  arms  and  legs,  can  float  and  propel  himself  for  long 
periods  with  perfect  safety  and  with  comparatively  little  exer- 
tion. He  can  also  assume  the  vertical  position,  and  by  remain- 
ing perfectly  motionless,  or  by  treading  the  water  with  his 
feet,  can  prevent  himself  from  sinking ;  nay  more,  he  can  turn 
a  somersault  in  the  water  either  in  a  forward  or  backward 


PROGRESSION  ON  AND  IN  THE  WATER. 


81 


direction.  The  position  most  commonly  assumed  in  swim- 
ming is  the  prone  one,  where  the  ventral  surface  of  the  body 
is  directed  towards  the  water.  In  this  case  the  anterior  and 
posterior  extremities  are  simultaneously  flexed  and  drawn 
towards  the  body  slowly,  after  which  they  are  simultaneously 
and  rapidly  extended.  The  swimming  of  the  frog  conveys  an 
idea  of  the  movement.1  In  ordinary  swimming,  when  the 
anterior  and  posterior  extremities  are  simultaneously  flexed, 
and  afterwards  simultaneously  extended,  the  hands  and  feet 
describe  four  ellipses;  an  arrangement  which,  as  explained, 
increases  the  area  of  support  furnished  by  the  moving  parts. 
The  ellipses  are  shown  at  fig.  38 ;  the  continuous  lines  repre- 
senting extension,  the  dotted  lines  flexion. 


Fig.  88. 


Pig.  40. 


Thus  when  the  arms  and  legs  are  pushed  away  from  the 
body,  the  arms  describe  the  inner  sides  of  the  ellipses  (fig. 
38,  a  a),  the  legs  describing  the  outer  sides  (c  c).  When  the 
arms  and  le.gs  are  drawn  towards  the  body,  the  arms  describe 
the  outer  sides  of  the  ellipses  (b  I),  the  legs  describing  the 
inner  sides  (d  d).  As  the  body  advances,  the  ellipses  are  opened 
out  and  loops  formed,  as  at  e  e,  ff  of  fig.  39.  If  the  speed 
attained  is  sufficiently  high,  the  loops  are  converted  into 

1  The  frog  in  swimming  leisurely  frequently  causes  its  extremities  to  move 
diagonally  and  alternately.  When,  however,  pursued  and  alarmed,  it  folds 
its  fore  legs,  and  causes  its  hind  ones  to  move  simultaneously  and  with  great 
vigour  by  a  series  of  sudden  jerks,  similar  to  those  made  by  man  when 
swimming  on  his  back. 


82      •  ANIMAL  LOCOMOTION. 

waved  lines,  as  in  walking  and  flying. — (Fide  gg,hh  of  fig. 
40,  p.  81,  and  compare  with  fig.  18,  p.  37,  and  figs.  71  and  73, 
p.  144.)  The  swimming  of  man,  like  the  walking,  swimming, 
and  flying  of  animals,  is  effected  by  alternately  flexing  and 
extending  the  limbs,  as  shown  more  particularly  at  fig.  41, 
A,  B,  C. 


Fio.  41. — A  shows  the  arms  and  legs  folded  or  flexed  and  drawn  towards  the 
inrsi.i]  line  of  the  body.  —Origiiml. 

B  shows  the  anus  and  legs  opened  out  or  extended  and  carried  away  from 
the  mesial  line  of  the  Ixxly.  —Original. 

C  shows  the  arms  and  legs  in  an  intermediate  position,  i.e.  when  they  are 
neither  flexed  nor  extended.  The  arms  and  legs  require  to  be  in  the  posi- 
tion shown  at  A  before  they  can  assume  that  represented  at  B,  and  they 
require  to  be  in  the  position  shown  at  B  before  they  can  .assume  that 
represented  at  C.  When  the  arms  and  legs  are  successively  assuming  the 
positions  indicated  at  A,  B,  and  C,  they  move  in  ellipses,  as  explained. — 
Original. 

By  alternately  flexing  and  extending  the  limbs,  the  angles 
made  by  their  several  parts  with  each  other  are  decreased 
and  increased, — an  arrangement  which  diminishes  and  aug- 
ments the  degree  of  resistance  experienced  by  the  swimming 
surfaces,  which  by  this  means  are  made  to  elude  and  seize 
the  water  by  turns.  This  result  is  further  secured  by  the 
limbs  being  made  to  move  more  slowly  in  flexion  than  in 
extension,  and  by  the  limbs  being  made  to  rotate  in  the 
direction  of  their  length  in  such  a  manner  as  to  diminish  the 
resistance  experienced  during  the  former  movement,  and 
increase  it  during  the  latter.  When  the  arms  are  extended, 
the  palms  of  the  hands  and  the  inner  surfaces  of  the  arms 
are  directed  downwards,  and  assist  in  buoying  up  the 
anterior  portion  of  the  body.  The  hands  are  screwed 
slightly  round  towards  the  end  of  extension,  the  palms  acting 


PROGRESSION  ON  AND  IN  THE  WATER.  83 

in  an  outward  and  backward  direction  (fig.  41,  B).  In  this 
movement  the  posterior  surfaces  of  the  arms  take  part ;  the 
palms  and  posterior  portions  of  the  arms  contributing  to  the 
propulsion  of  "the  body.  When  the  arms  are  flexed,  the  flat 
of  the  hands  is  directed  downwards  (fig.  41,  C).  Towards 
the  end  of  flexion  the  hands  are  slightly  depressed,  which  has 
the  effect  of  forcing  the  body  upwards,  and  hence  the  bobbing 
or  vertical  wave-movement  observed  in  the  majority  of  swim- 
mers.1 

During  flexion  the  posterior  surfaces  of  the  arms  act 
powerfully  as  propellers,  from  the  fact  of  their  striking  the 
water  obliquely  in  a  backward  direction.  I  avoid  the  terms 
lack  and  forward  strokes,  because  the  arms  and  hands,  so  long 
as  they  move,  support  and  propel.  There  is  no  period  either 
in  extension  or  flexion  in  which  they  are  not  effective. 
When  the  legs  are  pushed  away  from  the  body,  or  extended 
(a  movement  which  is  effected  rapidly  and  with  great  energy, 
as  shown  at  fig.  41,  E),  the  soles  of  the  feet,  the  anterior  sur- 
faces of  the  legs,  and  the  posterior  surfaces  of  the  thighs,  are 
directed  outwards  and  backwards.  This  enables  them  to 
seize  the  water  with  great  avidity,  and  to  propel  the  body 
forward.  The  efficiency  of  the  legs  and  feet  as  propelling 
organs  during  extension  is  increased  by  their  becoming  more 
or  less  straight,  and  by  their  being  moved  with  greater 
rapidity  than  in  flexion ;  there  being  a  general  back-thrust  of 
the  limbs  as  a  whole,  and  a  particular  back-thrust  of  their 
several  parts.2  In  this  movement  the  inner  surfaces  of  the 
legs  and  thighs  act  as  sustaining  organs  and  assist  in  floating 
the  posterior  part  of  the  body.  The  slightly  inclined  position 
of  the  body  in  the  water,  and  the  forward  motion  acquired  in 
swimming,  contribute  to  this  result.  When  the  legs  and  feet 
are  drawn  towards  the  body  or  flexed,  as  seen  at  fig.  41,  (7,  A, 

1  The  professional  swimmer  avoids  bobbing,  and  rests  the  side  of  his  head 
on  the  water  to  diminish  its  weight  and  increase  speed. 

2  The  greater  power  possessed  by  the  limbs  during  extension,  and  more 
especially  towards  the  end  of  extension,  is  well  illustrated  by  the  kick  of 
the  horse  ;  the  hind  feet  dealing  a  terrible  blow  when  they  have  reached  their 
maximum  distance  from  the  body.     Ostlers  are  well  aware  of  this  fact,  and 
in  grooming  a  horse  keep  always  very  close  to  his  hind  quarters,  so  that  if 
he  does  throw  up  they  are  forced  back  but  not  injured. 


84  ANIMAL  LOCOMOTION. 

their  movements  are  slowed,  an  arrangement  which  reduces 
the  degree  of  friction  experienced  by  the  several  parts  of  the 
limbs  when  they  are,  as  it  were,  being  drawn  off  the  water 
preparatory  to  a  second  extension. 

There  are  several  grave  objections  to  the  ordinary  or  old 
method  of  swimming  just  described.'  1st,  The  body  is  laid 
prone  on  the  water,  which  exposes  a  large  resisting  surface 
(fig.  41,  A,  B,  C,  p.  82).  2d,  The  arms  and  legs  are  spread 
out  on  either  side  of  the  trunk,  so  that  they  are  applied  very 
indirectly  as  propelling  organs  (fig.  41,  B,  C).  3d,  The  most 
effective  part  of  the  stroke  of  the  arms  and  legs  corresponds 
to  something  like  a  quarter  of  an  ellipse,  the  remaining  three 
quarters  being  dedicated  to  getting  the  arms  and  legs  into 
position.  This  arrangement  wastes  power  and  greatly  in- 
creases friction ;  the  attitudes  assumed  by  the  body  at  B  and 
C  of  fig.  4 1  being  the  worst  possible  for  getting  through  the 
water.  4th,  The  arms  and  legs  are  drawn  towards  the  trunk 
the  one  instant  (fig.  41,  A),  and  pushed  away  from  it  the  next 
(fig.  41,  B).  This  gives  rise  to  dead  points,  there  being  a 
period  when  neither  of  the  extremities  are  moving.  The 
body  is  consequently  impelled  by  a  series  of  jerks,  the  swim- 
ming mass  getting  up  and  losing  momentum  between  the 
strokes. 

In  order  to  remedy  these  defects,  scientific  swimmers  have 
of  late  years  adopted  quite  another  method.  Instead  of 
working  the  arms  and  legs  together,  they  move  first  the  arm 
and  leg  of  one  side  of  the  body,  and  then  the  arm  and  leg  of 
the  opposite  side.  This  is  known  as  the  overhand  movement, 
and  corresponds  exactly  with  the  natural  walk  of  the  giraffe, 
the  amble  of  the  horse,  and  the  swimming  of  the  sea-bear. 
It  is  that  adopted  by  the  Indians.  In  this  mode  of  swimming 
the  body  is  thrown  more  or  less  on  its  side  at  each  stroke, 
the  body  twisting  and  rolling  in  the  direction  of  its  length, 
as  shown  at  fig.  42,  an  arrangement  calculated  greatly  to 
reduce  the  amount  of  friction  experienced  in  forward  motion. 

The  overhand  movement  enables  the  swimmer  to  throw 
himself  forward  on  the  water,  and  to  move  his  arms  and  legs 
in  a  nearly  vertical  instead  of  a  horizontal  plane;  the  ex- 
tremities working,  as  it  were,  above  and  beneath  the  trunk, 


PROGRESSION  ON  AND  IN  THE  WATER.  85 

rather  than  on  either  side  of  it.  The  extremities  are  con- 
sequently employed  in  the  best  manner  possible  for  developing 
their  power  and  reducing  the  friction  to  forward  motion 
caused  by  their  action.  This  arrangement  greatly  increases 
the  length  of  the  effective  stroke,  both  of  the  arms  and  legs, 
this  being  equal  to  nearly  half  an  ellipse.  Thus  when  the 
left  arm  and  leg  are  thrust  forward,  the  arm  describes  the 
curve  a  b  (fig.  42),  the  leg  e  describing  a  similar  curve.  As 
the  right  side  of  the  body  virtually  recedes  when  the  left 
side  advances,  the  right  arm  describes  the  curve  c  d,  while 
the  left  arm  is  describing  the  curve  a  b;  the  right  leg  / 
describing  a  curve  the  opposite  of  that  described  by  e  (com- 
pare arrows).  The  advancing  of  the  right  and  left  sides  of 


FIG.  42. —Overhand  Swimming. — Original. 

the  body  alternately,  in  a  nearly  straight  line,  greatly  con- 
tributes to  continuity  of  motion,  the  impulse  being  applied 
now  to  the  right  side  and  now  to  the  left,  and  the  limbs 
being  disposed  and  Avorked  in  such  a  manner  as  in  a  great 
measure  to  reduce  friction  and  prevent  dead  points  or  halts. 
When  the  left  arm  and  leg  are  beiiig  thrust  forward  (a  b,  e 
of  fig.  42),  the  right  arm  and  leg  strike  very  nearly  directly 
backward  (c  d,  f  of  fig.  42).  The  right  arm  and  leg,  and  the 
resistance  which  they  experience  from  the  water  consequently 
form  a  point  tfappui  for  the  left  arm  and  leg  ;  the  two  sides 
of  the  body  twisting  and  screwing  upon  a  moveable  fulcrum 
(the  water) — an  arrangement  which  secures  a  maximum  of 
propulsion  with  a  minimum  of  resistance  and  a  minimum  of 
slip.  The  propulsive  power  is  increased  by  the  concave  surfaces 
of  the  hands  and  feet  being  directed  backwards  during  the  back 
stroke,  and  by  the  arms  being  made  to  throw  their  back 
water  in  a  slightly  outward  direction,  so  as  not  to  impede 
the  advance  of  the  legs.  The  overhand  method  of  swimming 


86  ANIMAL  LOCOMOTION. 

is  the  most  expeditious  yet  discovered,  hut  it  is  fatiguing,  and 
can  only  be  indulged  in  for  short  distances. 

An  improvement  on  the  foregoing  for  long  distances  is 
that  known  as  the  side  stroke.  In  this  method,  as  the  term 
indicates,  the  body  is  thrown  more  decidedly  upon  the  side. 
Either  side  may  be  employed,  some  preferring  to  swim  on  the 
right  side,  and  some  on  the  left ;  others  swimming  alternately 
on  the  right  and  left  sides.  In  swimming  \>y  the  side  stroke 
(say  on  the  left  side),  the  left  arm  is  advanced  in  a  curve, 
and  made  to  describe  the  upper  side  of  an  ellipse,  as  repre- 
sented at  a  b  of  fig.  43.  This  done,  the  right  arm  and  legs  are 
employed  as  propellers,  the  right  arm  and  legs  making  a 
powerful  backward  stroke,  in  which  the  concavity  of  the  hand 


Fio.  43.— Side-stroke  Swimming. — Original. 

is  directed  backwards  and  outwards,  as  shown  at  c  d  of  the 
same  figure.1  The  right  arm  in  this  movement  describes 
the  under  side  of  an  ellipse,  and  acts  in  a  nearly  vertical 
plane.  When  the  right  arm  and  legs  are  advanced,  some 
swimmers  lift  the  right  arm  out  of  the  water,  in  order  to 
diminish  friction — the  air  being  more  easily  penetrated 
than  the  water.  The  lifting  of  the  arm  out  of  the  water 
increases  the  speed,  but  the  movement1  is  neither  graceful 
nor  comfortable,  as  it  immerses  the  head  of  the  swimmer 
at  each  stroke.  Others  keep  the  right  arm  in  the  water 
and  extend  the  arm  and  hand  in  such  a  manner  as  to 
cause  it  to  cut  straight  forward.  In  the  side  stroke  the  left 
arm  (if  the  operator  swims  on  the  left  side)  acts  as  a  cutwater 
(fig.  43,  b).  It  is  made  to  advance  when  the  right  arm 

1  The  outward  direction  given  to  the  ami  and  hand  enables  then  to  force 
away  the  back  water  from  the  body  and  limbs,  and  so  reduce  the  friction  to 
forward  »otion. 


PROGRESSION  ON  AND  IN  THE  WATER.  87 

and  legs  are  forced  backwards  (fig.  43,  c  d).  The  right  arm 
and  legs  move  together,  and  alternate  with  the  left  arm, 
which  moves  by  itself.  The  right  arm  and  legs  are  flexed 
and  carried  forwards,  while  the  left  arm  is  extended  and 
forced  backwards,  and  vice  versd.  The  left  arm  always  moves 
in  an  opposite  direction  to  the  right  arm  and  legs.  We  have 
thus  in  the  side  stroke  three  limbs  moving  together  in  the 
same  direction  and  keeping  time,  the  fourth  limb  always 
moving  in  an  opposite  direction  and  out  of  time  with  the 
other  three.  The  limb  which  moves  out  of  time  is  the  left 
one  if  the  operator  swims  on  the  left  side,  and  the  right  one 
if  he  swims  on  the  right  side.  In  swimming  on  the  left 
side,  the  right  arm  and  legs  are  advanced  slowly  the  one 
instant,  and  forced  in  a  backward  direction  with  great  energy 
and  rapidity  the  next.  Similar  remarks  are  to  be  made  re- 
garding the  left  arm.  When  the  right  arm  and  legs  strike 
backwards  they  communicate  to  the  body  a  powerful  forward 
impulse,  which,  seeing  the  body  is  tilted  upon  its  side  and 
advancing  as  on  a  keel,  transmits  it  to  a  considerable  distance. 
This  arrangement  reduces  the  amount  of  resistance  to  forward 
motion,  conserves  the  energy  of  the  swimmer,  and  secures  in  a 
great  measure  continuity  of  movement,  the  body  being  in  the 
best  possible  position  for  gliding  forward  between  the  strokes. 
In  good  side  swimming  the  legs  are  made  to  diverge 
widely  when  they  are  extended  or  pushed  away  from  the 
body,  so  as  to  include  within  them  a  fluid  wedge,  the  apex  of 
which  is  directed  forwards.  When  fully  extended,  the  legs 
are  made  to  converge  in  such  a  manner  that  they  force  the 
body  away  from  the  wedge,  and  so  contribute  to  its  propul- 
sion. By  this  means  the  legs  in  extension  are  made  to 
give  what  may  be  regarded  a  double  stroke,  viz.  an  outward 
and  inward  one.  When  the  double  move  has  been  made, 
the  legs  are  flexed  or  drawn  towards  the  body  preparatory  to 
a  new  stroke.  In  swimming  on  the  left  side,  the  left  or 
cutwater  arm  is  extended  or  pushed  away  from  the  body  in 
such  a  manner  that  the  concavity  of  the  left  hand  is  directed 
forwards,  and  describes  the  upper  half  of  a  vertical  ellipse. 
It  thus  meets  with  comparatively  little  resistance  from  the 
water.  When,  however,  the  left  arm  is  flexed  and  drawn 


88  ANIMAL  LOCOMOTION. 

towards  the  body,  the  concavity  of  the  left  hand  is  directed 
backwards  and  made  to  describe  the  under  half  of  the  ellipse, 
so  as  to  scoop  and  seize  the  water,  and  thus  contribute  to  the 
propulsion  of  the  body.  The  left  or  cutwater  arm  materially 
assists  in  floating  the  anterior  portions  of  the  body.  The 
stroke  made  by  the  left  arm  is  equal  to  a  quarter  of  a  circle, 
that  made  by  the  right  arm  to  half  a  circle.  The  right 
arm,  when  the  operator  swims  upon  the  left  side,  is  con- 
sequently the  more  powerful  propeller.  The  right  arm, 
like  the  left,  assists  in  supporting  the  anterior  portion  of 
the  body.  In  swimming  on  the  left  side  the  major  pro- 
pelling factors  are  the  right  arm  and  hand  and  the  right 
and  left  legs  and  feet.  Swimming  by  the  side  stroke  is, 
on  the  whole,  the  most  useful,  graceful,  and  effective  yet 
devised.  It  enables  the  swimmer  to  make  headway  against 
wind,  wave,  and  tide  in  quite  a  remarkable  manner.  In- 
deed, a  dexterous  side-stroke  swimmer  can  progress  when 
a  powerful  breast-swimmer  would  be  driven  back.  In 
still  water  an  expert  non-professional  swimmer  ought  to 
make  a  mile  in  from  thirty  to  thirty-five  minutes.  A  pro- 
fessional swimmer  may  greatly  exceed  this.  Thus,  Mr.  J.  B. 
Johnson,  when  swimming  against  time,  August  5th,  1872,  in 
the  fresh-water  lake  at  Heudon,  near  London,  did  the  full 
mile  in  twenty-six  minutes.  The  first  half-mile  was  done  in 
twelve  minutes.  Cceteris  paribus,  the  shorter  the  distance,  the 
greater  the  speed.  In  August  1868,  Mr.  Harry  Parker,  a 
well-known  professional  swimmer,  swam  500  yards  in  the 
Serpentine  in  seven  minutes  fifty  •  seconds.  Among  non- 
professional  swimmers  the  performance  of  Mr.  J.  B.  Booth 
is  very  creditable.  This  gentleman,  in  June  1871,  swam 
440  yards  in  seven  minutes  fourteen  seconds  in  the  fresh- 
water lake  at  Hendon,  already  referred  to.  I  am  indebted 
for  the  details  regarding  time  to  Mr.  J.  A.  Cowan  of 
Edinburgh,  himself  acknowledged  to  be  one  of  the  fastest 
swimmers  in  Scotland.  The  speed  attained  by  man  in  the 
water  is  not  great  when  his  size  and  power  are  taken  into 
account.  It  certainly  contrasts  very  unfavourably  with  that 
of  seals,  and  still  more  unfavourably  with  that  of  fishes. 
This  is  clue  to  his  small  hands  and  feet,  the  slow  movements 


PBOGBESSION  ON  AND  IN  THE  WATER. 


89 


of  his  arms  and  legs,  and  the  awkward  manner  in  which  they 
are  applied  to  and  withdrawn  from  the  water. 

Swimming  of  the  Turtle,  Triton,  Crocodile,  etc. — The  swim- 
ming of  the  turtle  differs  in  some  respects  from  all  the  other 
forms  of  swimming.  While  the  anterior  extremities  of  this 


FIG.  44.— The  Turtle  (Chelonia  imbricata\  adapted  for  swimming  and  diving, 
the  extremities  being  relatively  larger  than  in  the  seal,  sea-bear,  and  wal- 
rus. The  anterior  extremities  have  a  thick  anterior  margin  and  a  thin 
posterior  one,  and  in  this  respect  resemble  wings.  Compare  with  figs.  86 
and  37,  pp.  74  and  76. — Original. 

quaint  animal  move  -alternately,  and  tilt  or  partially  rotate 
during  their  action,  as  in  the  sea-bear  and  walrus,  the  posterior 


FIG.  45.  -The  Crested  Newt  (Trilnn  cris.to.tvs,  Lsiur.)  In  the  newt  a  tail  is 
•nperadded  to  the  extremities,  the  tail  and  the  extremities  both  acting  in 
swimming.— Original. 

extremities  likewise  move  by  turns.  As,  moreover,  the  right 
anterior  and  left  posterior  extremities  move  together,  and  re- 
ciprocate with  the  left  anterior  and  right  posterior  ones,  the 
creature  has  the  appearance  of  walking  in  the  water  (fig.  44). 


90  ANIMAL  LOCOMOTION. 

The  same  remarks  apply  to  the  movements  of  the  extremi- 
ties of  the  triton  (fig.  45,  p.  89)  and  crocodile,  when  swimming, 
and  to  the  feebly  developed  corresponding  members  in  the 
lepidosiren,  proteus,  and  axolotl,  specimens  of  all  of  which  are 
to  be  seen  in  the  Zoological  Society's  Gardens,  London. 
In  the  latter,  natation  is  effected  principally,  if  not  altogether, 
by  the  tail  and  lower  half  of  the  body,  which  is  largely  de- 
veloped and  flattened  laterally  for  this  purpose,  as  in  the  fish. 

The  muscular  power  exercised  by  the  fishes,  the  cetaceans, 
and  the  seals  in  swimming,  is  conserved  to  a  remarkable 
extent  by  the  momentum  which  the  body  rapidly  acquires — 
the  velocity  attained  by  the  mass  diminishing  the  degree  of 
exertion  required  in  the  individual  or  integral  parts.  This 
holds  true  of  all  animals,  whether  they  move  on  the  land  or 
on  or  in  the  water  or  air. 

The  animals  which  furnish  the  connecting  link  between 
the  water  and  the  air  are  the  diving-birds  on  the  one  hand, 
and  the  flying-fishes  on  the  other, — the  former  using  their 
wings  for  flying  above  and  through  the  water,  as  occasion 
demands ;  the  latter  sustaining  themselves  for  considerable 
intervals  in  the  air  by  means  of  their  enormous  pectoral  fins. 

Flight  under  water,  etc. — Mr.  Macgillivray  thus  describes  a 
flock  of  red  mergansers  which  he  observed  pursuing  sand-eels 
in  one  of  the  shallow  sandy  bays  of  the  Outer  Hebrides  : — 
"  The  birds  seemed  to  move  under  the  water  with  almost  as 
much  velocity  as  in  the  air,  and  often  rose  to  breathe  at  a 
distance  of  200  yards  from  the  spot  at  which  they  had 
dived."1 

In  birds  which  fly  indiscriminately  above  and  beneath  the 
water,  the  wing  is  provided  with  stiff  feathers,  and  reduced 
to  a  minimum  as  regards  size.  In  subaqueous  flight  the 
wings  may  act  by  themselves,  as  in  the  guillemots,  or  in  con- 
junction with  the  feet,  as  in  the  grebes.2  To  convert  the 

1  History  of  British  Birds,  vol.  i.  p.  48. 

*  The  guillemots  in  diving  do  not  use  their  feet ;  so  that  they  literally  fly 
under  the  water.  Their  wings  for  this  purpose  are  reduced  to  the  smallest 
possible  dimensions  consistent  with  night.  The  loons,  on  the  other  hand, 
while  they  employ  their  feet,  rarely,  if  ever,  use  their  wings.  The  sub- 
aqueous progression  of  the  grebe  resembles  that  of  the  rog.— Cuvier's  Animal 
Kingdom,  Loncl.  1840,  pp.  252,  253. 


PROGRESSION  ON  AND  IN  THE  WATER. 


91 


wing  into  a  powerful  oar  for  swimming,  it  is  only  necessary 
to  extend  and  flex  it  in  a  slightly  backward  direction,  the 
mere  act  of  extension  causing  the  feathers  to  roll  down,  and 
giving  to  the  back  of  the  wing,  which  in  this  case  communi- 
cates the  more  effective  stroke,  the  angle  or  obliquity  neces- 
sary for  sending  the  animal  forward.  This  angle,  I  may 
observe,  corresponds  with  that  made  by  the  foot  during  ex- 
tension, so  that,  if  the  feet  and  wings  are  both  employed, 
they  act  in  harmony.  If  proof  were  wanting  that  it  is  the 
back  or  convex  surface  of  the  wing  which  gives  the  more 
effective  stroke  in  subaquatic  flight,  it  would  be  found  in  the 
fact  that  in  the  penguin  and  great  auk,  which  are  totally  in- 
capable of  flying  out  of  the  water,  the  wing  is  actually  twisted 


FIG.  46.— The  Little  Penguin  (Aptcnodytes  minor,  Linti.},  adapted  exclusively 
for  swimming  and  diving.  In  this  quaint  nird  the  wing  forms  a  perfect 
screw,  and  is  employed  as  such  in  swimming  and  diving.  Compare  with 
fig.  37,  p.  70,  and  tig.  44,  p.  89.  —  Original. 

round  in  order  that  the  concave  surface,  which  takes  a  better 
hold  of  the  water,  may  be  directed  backwards  (fig.  4G).1  'The 
thick  margin  of  the  wing  when  giving  the  effective  stroke 
is  turned  downwards,  as  happens  in  the  flippers  of  the 
sea-bear,  walrus,  and  turtle^  This,  I  need  scarcely  remark,  is 
precisely  the  reverse  of  what  occurs  in  the  ordinary  wing  in 
aerial  flight.  In  those  extraordinary  birds  (great  auk  and 
penguin)  the  wing  is  covered  with  short,  bristly-looking 
feathers,  and  is  a  mere  rudiment  and  exceedingly  rigid,  the 

1  In  the  swimming  of  tlie  crocodile,  turtle,  triton,  and  frog,  the  concave 
surfaces  of  the  feet  of  the  anterior  extremities  are  likewise  turned  backward* 


92  ANIMAL  LOCOMOTION. 

movement  which  wields  it  emanating,  for  the  most  part,  from 
the  shoulder,  where/ the  articulation  partakes  of  the  nature  of 
a  universal  joint.  £Che  wing  is  beautifully  twisted  upon  itself, 
and  when  it  is  elevated  and  advanced,  it  rolls  up  from  the 
side  of  the  bird  at  varying  degrees  of  obliquity,  till  it  makes 
a  right  angle  Avith  the  body,  when  it  presents  a  narrow  or 
cutting  edge  to  the  Avater.  The  wing  when  fully  extended, 
as  in  ordinary  flight,  makes,  on  the  contrary,  an  angle  of 
something  like  30°  Avith  the  horizon.  When  the  wing  is 
depressed  and  carried  backAvards,1  the  angles  which  its  under 
surface  make  with  the  surface  of  the  water  are  gradually 
increased.  The  wing  of  the  penguin  and  auk  propels  both 
Avhen  it  is  elevated  and  depressed.  It  acts  very  much  after 
the  manner  of  a  screw;  and  this,  as  I  shall  endeavour  to 
show,  holds  true  likewise  of  the  wing  adapted  for  aerial  flight. 
Difference  between  Subaquatic  and  Aerial  Flight. — The  differ- 
ence betAveen  subaquatic  flight  or  diving,  and  flight  proper, 
may  be  briefly  stated.  In  aerial  flight,  the  most  effective 
stroke  is  delivered  downwards  and  forwards  by  the  under, 
concave,  or  biting  surface  of  the  wing  which  is  turned  in  this 
direction ;  the  less  effective  stroke  being  delivered  in  an  up- 
Avard  and  forward  direction  by  the  upper,  convex,  or  non- 
biting  surface  of  the  wing.  In  subaquatic  flight,  on  the 
contrary,  the  most  effective  stroke  is  delivered  downwards  and 
backwards,  the  least  effective  one  upAvards  and  forwards.  In 
aerial  flight  the  long  axis  of  the  body  of  the  bird  and  the 
short  axis  of  the  wings  are  inclined  slightly  upwards,  and  make 
a  forward  angle  with  the  horizon.  In  subaquatic  flight  the 
long  axis  of  the  body  of  the  bird,  and  the  short  axis  of  the 
wings  are  inclined  slightly  dowmvards  and  make  a  backward 
angle  AAath  the  surface  of  the  water.  The  wing  acts  more  or  less 
efficiently  in  every  direction,  as  the  tail  of  the  fish  does.  The 
difference  noted  in  the  direction  of  the  down  stroke  in  flying 
and  diving,  is  rendered  imperative  by  the  fact  that  a  bird  which 
flies  in  the  air  is  heavier  than  the  medium  it  navigates,  and 
must  be  supported  by  the  wings ;  Avhereas  a  bird  which  flies 
under  the  Avater  or  dives,  is  lighter  than  the  Avater,  and  must 

1  Tlie  effective  stroke  is  also  delivered  during  flexion  in  the  shrimp,  prawn, 

ami  lol»ter. 


PROGRESSION  ON  AND  IN  THE  WATER.  93 

force  itself  into  it  to  prevent  its  being  buoyed  up  to  the  sur- 
face. However  paradoxical  it  may  seem,  weight  is  necessary 
to  aerial  flight,  and  levity  to  subaquatic  flight.  A  bird  destined 
to  fly  above  the  water  is  provided  with  travelling  surfaces,  so 
fashioned  and  so  applied  (they  strike  from  above,  downward* 
.ma  j<>ncardx),  that  if  it  was  lighter  than  the  air,  they  would 
carry  it  off  into  space  without  the  possibility  of  a  return ;  in 
other  words,  the  action  of  the  wings  would  carry  the  bird 
obliquely  upwards,  and  render  it  quite  incapable  of  flying 
either  in  a  horizontal  or  downward  direction.  In  the  same 
way,  if  a  bird  destined  to  fly  under  the  water  (auk  and  pen- 
guin) was  not  lighter  than  the  water,  such  is  the  configuration 
and  mode  of  applying  its  travelling  surfaces  (they  strike  from 
above,  downwards  and  backwards),  they  would  carry  it  in  the 
direction  of  the  bottom  without  any  chance  of  return  to  the 
surface.  In  aerial  flight,  weight  is  the  power  which  nature 
has  placed  at  the  disposal  of  the  bird  for  regulating  its  alti- 
tude and  horizontal  movements,  a  cessation  of  the  play  of  its 
wings,  aided  by  the  inertia  of  its  trunk,  enabling  the  bird  to 
approach  the  earth.  In  subaquatic  flight,  levity  is  a  power 
furnished  for  a  similar  but  opposite  purpose ;  this,  combined 
with  the  partial  slowing  or  stopping  of  the  wings  and  feet, 
enabling  the  diving  bird  to  regain  the  surface  at  any  moment. 
Levity  and  weight  are  auxiliary  forces,  but  they  are  necessary 
forces  when  the  habits  of  the  aerial  and  aquatic  birds  and  the 
form  and  mode  of  applying  their  travelling  surfaces  are  taken 
into  account.  If  the  aerial  flying  bird  was  lighter  than  the  air, 
its  wings  would  require  to  be  twisted  round  to  resemble  the  diving 
wings  of  the  penguin  and  auk.  If,  on  the  other  hand,  the  diving 
bird  (penguin  or  auk)  was  heavier  than  the  water,  its  wings 
would  require  to  resemble  aerial  wings,  and  they  would  require 
to  strike  in  an  opposite  direction  to  that  in  which  they  strike 
normally.  From  this  it  follows  that  weight  is  necessary  to  the 
bird  (as  at  present  constructed)  destined  to  navigate  the  air,, 
and  levity  to  that  destined  to  navigate  the  water.  If  a  bird 
was  made  very  large  and  very  light,  it  is  obvious  that  the 
diving  force  at  its  disposal  would  be  inadequate  to  submerge 
it.  If,  again,  it  was  made  very  small  and  very  heavy,  it  is 
equally  plain  that  it  could  not  fly.  Nature,  however,  has 


ANIMAL  LOCOMOTION. 


struck  the  just  balance ;  she  has  made  the  diving  bird,  which 
flies  under  the  \vater,  relatively  much  heavier  than  the  bird 


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which  flies  in  the  air,  and  has  curtailed  the  travelling  surfaces 
of  the  fonnL-r,  while  she  has  increased  those  of  the  latter. 


PKOGKESSION  ON  AND  IN  THE  WATER.  95 

For  the  same  reason,  she  has  furnished  the  diving  bird  with 
a  certain  degree  of  buoyancy,  and  the  flying  bird  with  a  cer- 
tain amount  of  weight — levity  tending  to  bring  the  one  to 
the  surface  of  the  water,  weight  the  other  to  the  surface  of 
the  earth,  which  is  the  normal  position  of  rest  for  both.  The 
action  of  the  subaquatic  or  diving  wing  of  the  king  penguin 
is  well  seen  at  p.  94,  fig.  47. 

From  what  has  been  stated  it  will  be  evident  that  the 
wing  acts  very  differently  in  and  out  of  the  water ;  and  this 
is  a  point  deserving  of  attention,  the  more  especially  as  it 
seems  to  have  hitherto  escaped  observation.  In  the  water 
the  wing,  when  most  effective,  strikes  downwards  and  backwards, 
and  acts  as  an  auxiliary  of  the  foot ;  whereas  in  the  air  it 
strikes  downwards  and  forwards.  The  oblique  surfaces,  spiral 
or  otherwise,  presented  by  animals  to  the  water  and  air  are 
therefore  made  to  act  in  opposite  directions,  as  far  as  the 
down  strokes  are  concerned.  This  is  owing  to  the  greater 
density  of  the  water  as  compared  with  the  air, — the  former 
supporting  or  nearly  supporting  the  animal  moving  upon  or 
in  it ;  the  latter  permitting  the  creature  to  fall  through  it  in  a 
downward  direction  during  the  ascent  of  the  wing.  To  coun- 
teract the  tendency  of  the  bird  in  motion  to  fall  downwards 
and  forwards,  the  down  stroke  is  delivered  in  this  direction  ; 
the  kite-like  action  of  the  wing,  and  the  rapidity  with  which 
it  is  moved  causing  the  mass  of  the  bird  to  pursue  a  more 
or  less  horizontal  course.  I  offer  this  explanation  of  the 
action  of  the  wing  in  and  out  of  the  water  after  repeated  and 
careful  observation  in  tame  and  wild  birds,  and,  as  I  am 
aware,  in  opposition  to  all  previous  writers  on  the  subject. 

The  rudimentary  wings  or  paddles  of  the  penguin  (the 
movements  of  which  I  had  an  opportunity  of  studying  in  a 
tame  specimen)  are  principally  employed  in  swimming  and 
diving.  The  feet,  which  are  of  moderate  size  and  strongly 
webbed,  are  occasionally  used  as  auxiliaries.  There  is  this 
difference  between  the  movements  of  the  wings  and  feet 
of  this  most  curious  bird,  and  it  is  worthy  of  attention. 
The  wings  act  together,  or  synchronously,  as  in  flying  birds ; 
the  feet,  on  the  other  hand,  are  moved  alternately.  The 
wings  are  wielded  with  great  energy,  and,  because  of  their 


96  ANIMAL  LOCOMOTION. 

semi-rigid  condition,  are  incapable  of  expansion.  They  there- 
fore present  their  maximum  and  minimum  of  surface  by 
a  partial  rotation  or  tilting  of  the  pinion,  as  in  the  walrus, 
sea-bear,  and  turtle.  The  feet,  which  are  moved  with  less 
vigour,  are,  on  the  contrary,  rotated  or  tilted  to  a  very  slight 
extent,  the  increase  and  diminution  of  surface  being  secured 
by  the  opening  and  closing  of  the  membranous  expansion  or 
web  between  the  toes.  In  this  latter  respect  they  bear  a  cer- 
tain analogy  to  the  feet  of  the  seal,  the  toes  of  which,  as  has 
been  explained,  spread  out  or  divaricate  during  extension, 
and  the  reverse.  The  feet  of  the  penguin  entirely  differ 
from  those  of  the  seal,  in  being  worked  separately,  the 
foot  of  one  side  being  flexed  or  drawn  towards  the  body, 


Fio.  48.— Swan,  in  the  act  of  swimming,  the  right  foot  being  fully  expanded, 
and  about  to  give  the  effective  stroke,  which  is  delivered  outwards,  down- 
wards, and  backwards,  as  represented  at.  r  of  fig.  50;  the  left  foot  being  closed, 
and  about  to  make  the  itturn  stioke,  which  is  delivered  in  an  inward,  up- 
ward, and  forward  direction,  as  shown  at  s  of  fig.  50.  In  rapid  swimming 
the  swan  flexes  its  legs  simultaneously  and  somewhat  slowly ;  it  then 
vigorously  extends  them.— Original. 

while  its  fellow  is  being  extended  or  pushed  away  from  it. 
The  feet,  moreover,  describe  definite  curves  in  opposite  direc- 
tions, the  right  foot  proceeding  from  within  outwards,  and 
from  above  downwards  during  extension,  or  when  it  is  fully 
expanded  and  giving  the  effective  stroke  ;  the  left  one,  which 
is  moving  at  the  same  time,  proceeding  from  without  in- 
wards and  from  below  upwards  during  flexion,  or  when  it  is 
folded  up,  as  happens  during  the  back  stroke.  In  the  acts  of 
extension  and  flexion  the  Tegs  are  slightly  rotated,  and  the 


PROGRESSION  ON  AND  IN  THE  WATER. 


97 


feet  more  or  less  tilted.  The  same  movements  are  seen  in  the 
feet  of  the  swan,  and  in  those  of  swimming  birds  generally 
(fig.  48). 

One  of  the  most  exquisitely  constructed  feet  for  swimming 
and  diving  purposes  is  that  of  the  grebe  (fig.  49).     This  foot 


Fir,.  49.— Foot  of  Grebe  (Podiceps).  In  this  foot  nach  toe  is  provided  with  its 
swimming  membrane  ;  the  membrane  being  closed  when  the  foot  is  Hexed, 
and  expanded  when  the  foot  is  extended.  Compare  witli  foot  of  swan  (fig. 
48),  where  the  swimming  membrane  is  continued,  from  the  one  toe  to  the 
other.— (After  Dallas.) 

consists  of  three  swimming  toes,  each  of  which  is  provided 
with  a  membranous  expansion,  which  closes  when  the  foot  is 
being  drawn  towards  the  body  during  the  back  stroke,  and 
opens  out  when  it  is  being  forced  away  from  the  body  during 
the  effective  stroke. 


Fio.  50.— Diagram  representing  the  double  waved  track  described  by  the  feet, 
nl  swimming  birds.  Compare  witlings.  18  and  19,  pp.  37  and  39,  and  with 
lig.  :i'2,  p.  ti.s!—  Original. 

Ill  swimming  birds,  each  foot  describes  one  side  of  an 
ellipse  when  it  is  extended  and  thrust  from  the  body,  the 
other  side  of  the  ellipse  being  described  when  the  foot  is  flexed 
and  drawn  towards  the  body.  The  curve  described  by  the  right 
foot  when  pushed  from  the  body  is  seen  at  the  arrow  r  of  fig. 
50  ;  that  formed  by  the  left  foot  when  drawn  towards  the 
body,  at  the  arrow  s  of  the  same  figure.  The  curves  formed 


98 


ANIMAL  LOCOMOTION. 


by  the  feet  during  extension  and  flexion  produce,  when  united 
in  the  act  of  swimming,  waved  lines,  these  constituting  a 
chart  for  the  movements  of  the  extremities  of  swimming  birds. 

There  is  consequently  an  obvious  analogy  between  the 
swimming  of  birds  and  the  walking  of  man  (compare  fig.  50, 
p.  97,  with  fig.  19,  p.  39) ;  between  the  walking  of  man  and 
the  walking  of  the  quadruped  (compare  figs.  18  and  19,  pp. 
37  and  39)  ;  between  the  walking  of  the  quadruped  and  the 
swimming  of  the  walrus,  sea-bear,  and  seal;  between  the 
swimming  of  the  seal,  whale,  dugong,  manatee,  and  porpoise, 
and  that  of  the  fish  (compare  fig.  32,  p.  G8,  with  figs.  18  and 
19,  pp.  37  and  39);  and  between  the  swimming  of  the  fish 
and  the  flying  of  the  insect,  bat,  and  bird  (compare  all  the 
foregoing  figures  with  figs.  71,  73,  and  81,  pp.  144  and  157). 

Flight  of  the  Fly  ing -fish ;  tJie  kite-like  action  of  the  Wings,  etc. — 
Whether  the  flying-fish  uses  its  greatly  expanded  pectoral  fins 


Fir,.  51.—  The  Flying-fish  (Emcn'tus  cxsiUens,  Linn.),  with  wings  expanded  and 
elevated  in  the  art  of  flight  (vide  arrows)  This  anomalous  and  interesting 
creature  is  adapted  both  for  swimming  and  flying.  The  swimming-tail  is 
consequently  retained,  and  the  pectoral  fins,  which  art  as  wings,  are 
enormously  increased  in  size. — Original. 

as  a  bird  its  wings,  or  only  as  parachutes,  has  not,  so  far  as  I 
am  aware,  been  determined  by  actual  observation.  Most  ob- 
servers are  of  opinion  that  these  singular  creatures  glide  up 
the  wind,  and  do  not  beat  it  after  the  manner  of  birds ;  so 
that  their  flight  (or  rather  leap)  is  indicated  by  the  arc  of  a 
circle,  the  sea  supplying  the  chord.  I  have  carefully  examined 
the  structure,  relations,  and  action  of  those  fins,  and  am  satis- 
fied in  my  own  mind  that  they  act  as  true  pinions  within 


PROGRESSION  ON  AND  IN  THE  WATER.  99 

certain  limits,  their  inadequate  dimensions  and  limited  range 
alone  preventing  them  from  sustaining  the  fish  in  the  air  for 
indefinite  periods.  When  the  fins  are  fully  flexed,  as  happens 
when  the  fish  is  swimming,  they  are  arranged  along  the  sides 
of  the  body ;  but  when  it  takes  to  the  air,  they  are  raised 
above  the  body  and  make  a  certain  angle  with  it.  In  being 
raised  they  are  likewise  inclined  forwards  and  outwards,  the 
fins  rotating  on  their  long  axes  until  they  make  an  angle  of 
something  like  30°  with  the  horizon — this  being,  as  nearly  as 
I  can  determine,  the  greatest  angle  made  by  the  wings  during 
the  down  stroke  in  the  flight  of  insects  and  birds. 

The  pectoral  fins,  or  pseudo-wings  of  the  flying-fish,  like 
all  other  wings,  act  after  the  manner  of  kites — the  angles  of 
inclination  which  their  under  surfaces  make  with  the  horizon 
varying  according  to  the  degree  of  extension,  the  speed  ac- 
quired, and  the  pressure  to  which  they  are  subjected  by  being 
carried  against  the  air.  When  the  flying-fish,  after  a  pre- 
liminary rush  through  the  water  (in  which  it  acquires  initial 
velocity),  throws  itself  into  the  air,  il  is  supported  and  carried 
forwards  by  the  kite-like  action  of  its  pinions  ; — this  action 
being  identical  with  that  of  the  boy's  kite  when  the  boy  runs, 
and  by  pulling  upon  the  string  causes  the  kite  to  glide  up- 
wards and  forwards.  In  the  case  of  the  boy's  kite  a  pulling 
force  is  applied  to  the  kite  in  front.  In  the  case  of  the  flying- 
fish  (and  everything  which  flies)  a  similar  force  is  applied  to 
the  kites  formed  by  the  wings  by  the  weight  of  the  flying 
mass,  which  always  tends  to  fall  vertically  downwards. 
Weight  supplies  a  motor  power  in  flight  similar  to  that 
supplied  by  the  leads  in  a  clock.  In  the  case  of  the  boy's 
kite,  the  hand  of  the  operator  furnishes  the  power;  in 
flight,  a  large  proportion  of  the  power  is  furnished  by 
the  weight  of  the  body  of  the  flying  creature.  It  is  a 
matter  of  indifference  how  a  kite  is  flown,  so  long  as  its 
under  surface  is  made  to  impinge  upon  the  air  over  which 
it  passes.1  A  kite  will  fly  effectually  when  it  is  neither 
acted  upon  by  the  hand  nor  a  weight,  provided  always 
there  is  a  stiff  breeze  blowing.  In  flight  one  of  two  things 

1  "  On  the  Various  Modes  of  Flight  in  relation  to  Aeronautics."    By  the 
Author. — Proceedings  of  the  Royal  Institution  of  Groat  Britain,  March  1867. 


1 00  ANIMAL  LOCOMOTION. 

is  necessary.  Either  the  under  surface  of  the  wings  must 
be  carried  rapidly  against  still  air,  or  the  air  must  rush 
violently  against  the  under  surface  of  the  expanded  nut 
motionless  wings.  Either  the  wings,  the  body  bearing  them, 
or  the  air,  must  be  in  rapid  motion  ;  one  or  other  must  be 
active.  To  this  there  is  no  exception.  To  fly  a  kite  in  still 
air  the  operator  must  run.  If  a  breeze  is  blowing  the  operator 
does  not  require  to  alter  his  position,  the  breeze  doing  the 
entire  work.  It  is  the  same  with  wings.  In  still  air  a  bird, 
or  whatever  attempts  to  fly,  must  flap  its  wings  energetically 
until  it  acquires  initial  velocity,  when  the  flapping  may  be 
discontinued ;  or  it  must  throw  itself  from  a  height,  in  which 
case  the  initial  velocity  is  acquired  by  the  weight  of  the  body 
acting  upon  the  inclined  planes  formed  by  the  motionless 
wings.  The  flapping  and  gliding  action  of  the  wings  consti- 
tute the  difference  between  ordinary  flight  and  that  known 
as  skimming  or  sailing  flight.  The  flight  of  the  flying-fish  is 
to  be  regarded  rather  as  ^an  example  of  the  latter  than  the 
former,  the  fish  transferring  the  velocity  acquired  by  the 
vigorous  lashing  of  its  tail  in  the  water  to  the  air, — an 
arrangement  which  enables  it  to  dispense  in  a  great  measure 
with  the  flapping  of  the  wings,  which  act  by  a  combined 
parachute  and  wedge  action.  In  the  flying-fish  the  flying-fin 
or  wing  attacks  the  air  from  beneath,  whilst  it  is  being  raised 
above  the  body.  It  has  no  downward  stroke,  the  position 
and  attachments  of  the  fin  preventing  it  from  descending 
beneath  the  level  of  the  body  of  the  fish.  In  this  respect  the 
flying-fin  of  the  fish  differs  slightly  from  the  wing  of  the 
insect,  bat,  and  bird.  The  gradual  expansion  and  raising  of 
the  fins  of  the  fish,  coupled  with  the  fact  that  the  fins  never 
descend  below  the  body,  account  for  the  admitted  absence  of 
beating,  and  have  no  doubt  originated  the  belief  that  the 
pectoral  fins  are  merely  passive  organs.  If,  however,  they  do 
not  act  as  true  pinions  within  the  limits  prescribed,  it  is  diffi- 
cult, and  indeed  impossible,  to  understand  how  such  small 
creatures  can  obtain  the  momentum  necessary  to  project  them 
a  distance  of  200  or  more  yards,  and  to  attain,  as  they  some- 
times do,  an  elevation  of  twenty  or  more  feet  above  the  water. 
Mr.  Swainson,  in  crossing  the  line  in  1816,  zealously  attempted 


PROGRESSION  ON  AND  IN  THE  WATER.  101 

to  discover  the  true  action  of  the  fius  in  question,  but  the 
flight  of  the  fish  is  so  rapid  that  he  utterly  failed.  He  gives 
it  as  his  opinion  that  flight  is  performed  in  two  ways, — first 
by  a  spring  or  leap,  and  second  by  the  spreading  of  the 
pectoral  fins,  which  are  employed  in  propelling  the  fish  in  a 
forward  direction,  either  by  flapping  or  by  a  motion  analogous 
to  the  skimming  of  swallows.  He  records  the  important  fact, 
that  the  flying-fish  can  change  its  course  after  leaving  the 
water,  which  satisfactorily  proves  that  the  fins  are  not  simply 
passive  structures.  Mr.  Lord,  of  the  Royal  Artillery,1  thus 
wiites  of  those  remarkable  specimens  of  the  finny  tribe  : — 
"  There  is  no  sight  more  charming  than  the  flight  of  a  shoal 
of  flying-fish,  as  they  shoot  forth  from  the  dark  green  wave 
in  a  glittering  throng,  like  silver  birds  in  some  gay  fairy  tale, 
gleaming  brightly  in  the  sunshine,  and  then,  with  a  mere 
touch  on  the  crest  of  the  heaving  billow,  again  flitting  onward 
reinvigorated  and  refreshed." 

Before  proceeding  to  a  consideration  of  the  graceful  and, 
in  some  respects,  mysterious  evolutions  of  the  denizens  of  the 
air,  and  the  far-stretching  pinions  by  which  they  are  pro- 
duced, it  may  not  be  out  of  place  to  say  a  few  words  in  re- 
capitulation regarding  the  extent  and  nature  of  the  surfaces 
by  which  progression  is  secured  on  land  and  on  or  in  the 
water.  This  is  the  more  necessary,  as  the  travelling-surfaces 
employed  by  animals  in  walking  and  swimming  bear  a  cer- 
tain, if  not  a  fixed,  relation  to  those  employed  by  insects,  bats, 
and  birds  in  flying.  On  looking  back,  we  are  at  once  struck 
with  the  fact,  remarkable  in  some  respects,  that  the  travelling- 
surfaces,  whether  feet,  flippers,  fins,  or  pinions,  are,  as  a  rule, 
increased  in  proportion  to  the  tenuity  of  the  medium  on  which 
they  are  destined  to  operate.  In  the  ox  (fig.  18,  p.  37)  we 
behold  a  ponderous  body,  slender  extremities,  and  unusually 
small  feet.  The  feet  are  slightly  expanded  in  the  otter  (fig.  1 2, 
p.  34),  and  considerably  so  in  the  ornithorhynchus  (fig.  11,  p. 
34).  The  travelling-area  is  augmented  in  the  seal  (fig.  14,  p. 
34  ;  fig.  36,  p.  74),  penguin  (figs.  46  and  47,  pp.  91  and  94), 
sea-bear  (fig.  37,  p.  76),  and  turtle  (fig.  44,  p.  89).  In  the 
triton  (fig.  45,  p.  89)  a  huge  swimming-tail  is  added  to  the 
1  Nature  and  Art,  November  1866,  p.  173. 

SANTA  BARBARA  COLLEGE  LIBRAE 

~~ 


102  ANIMAL  LOCOMOTION. 

feet — the  tail  becoming  larger,  and  the  extremities  (anterior) 
diminishing,  in  the  manatee  (fig.  34,  p.  73)  and  porpoise  (fig. 
33,  p.  73),  until  we  arrive  at  the  fish  (fig.  30,  p.  65),  where 
not  only  the  tail  but  the  lower  half  of  the  body  is  actively 
engaged  in  natation.  Turning  from  the  water  to  the  air,  we 
observe  a  remarkable  modification  in  the  huge  pectoral  fins 
of  the  flying-fish  (fig.  51,  p.  98),  these  enabling  the  creature 
to  take  enormous  leaps,  and  serving  as  pseudo-pinions.  Turn- 
ing in  like  manner  from  the  earth  to  the  air,  we  encounter 
the  immense  tegumentary  expansions  of  the  flying-dragon 
(fig.  15,  p.  35)  and  galeopithecus  (fig.  16,  p.  35),  the  floating 
or  buoying  area  of  which  greatly  exceeds  that  of  some  of  the 
flying  beetles. 

In  those  animals  which  fly,  as  bats  (fig.  17,  p.  36),  insects 
(figs.  57  and  58,  p.  124  and  125),  and  birds  (figs.  59  and  60, 
p.  126),  the  travelling  surfaces,  because  of  the  extreme  tenuity 
of  the  air,  are  prodigiously  augmented ;  these  in  many  instances 
greatly  exceeding  the  actual  area  of  the  body.  While,  therefore, 
the  movements  involved  in  walking,  swimming,  and  flying  are 
to  be  traced  in  the  first  instance  to  the  shortening  and  length- 
ening of  the  muscular,  elastic,  and  other  tissues  operating  on 
the  bones,  and  their  peculiar  articular  surfaces;  they  are  to 
be  referred  in  the  second  instance  to  the  extent  and  configu- 
ration of  the  travelling  areas — these  on  all  occasions  being 
accurately  adapted  to  the  capacity  and  strength  of  the  animal 
and  the  density  of  the  medium  on  or  in  which  it  is  intended 
to  progress.  Thus  the  laud  supplies  the  resistance,  and 
affords  the  support  necessary  to  prevent  the  small  feet  of 
land  animals  from  sinking  to  dangerous  depths,  while  the 
water,  immensely  less  resisting,  furnishes  the  peculiar  medium 
requisite  for  buoying  the  fish,  and  for  exposing,  without 
danger  and  to  most  advantage,  the  large  surface  contained 
in  its  ponderous  lashing  tail, — the  air,  unseen  and  unfelt, 
furnishing  that  quickly  yielding  and  subtle  element  in  which 
the  greatly  expanded  pinions  of  the  insect,  bat,  and  bird  are 
made  to  vibrate  with  lightning  rapidity,  discoursing,  as  they 
do  so,  a  soft  and  stirring  music  very  delightful  to  the  lovei 
of  nature. 


PROGRESSION  IN  OR  THROUGH  THE  AIR. 

THE  atmosphere,  because  of  its  great  tenuity,  mobility,  and 
comparative  imponderability,  presents  little  resistance  to 
bodies  passing  through  it  at  low  velocities.  If,  however,  the 
speed  be  greatly  accelerated,  the  passage  of  even  an  ordinary 
cane  is  sensibly  impeded. 

This  comes  of  the  action  and  reaction  of  matter,  the  resist- 
ance experienced  varying  according  to  the  density  of  the 
atmosphere  and  the  shape,  extent,  and  velocity  of  the  body 
acting  upon  it.  While,  therefore,  scarcely  any  impediment 
is  offered  to  the  progress  of  an  animal  in  motion,  it  is  often 
exceedingly  difficult  to  compress  the  air  with  sufficient  rapidity 
and  energy  to  convert  it  into  a  suitable  fulcrum  for  securing 
the  onward  impetus.  This  arises  from  the  fact  that  bodies 
moving  in  the  air  experience  the  minimum  of  resistance  and 
occasion  the  maximum  of  displacement.  Another  and  very 
obvious  difficulty  is  traceable  to  the  great  disparity  in  the 
weight  of  air  as  compared  with  any  known  solid,  this  in  the 
case  of  water  being  nearly  as  1000  to  1.  According  to  the 
density  of  the  medium  so  is  its  buoying  or  sustaining  power. 

The  Wing  a  Lever  of  the  Third  Order. — To  meet  the  pecu- 
liarities stated  above,  the  insect,  bat,  and  bird  are  furnished 
with  extensive  surfaces  in  the  shape  of  pinions  or  wings, 
which  they  can  apply  with  singular  velocity  and  power,  as 
levers  of  the  third  order  (fig.  3,  p.  20),1  at  various  angles,  or 
by  alternate  slow  and  sudden  movements,  to  obtain  the 

1  In  this  form  of  lever  the  power  is  applied  between  the  fulcrum  and  the 
weight  to  be  raised.  The  mass  to  be  elevated  is  the  body  of  the  insect,  bat, 
or  bird,— the  force  which  resides  in  the  living  pinion  (aided  by  the  inertia  of 
the  trunk)  representing  the  power,  and  the  air  the  fulcrum. 


106  ANIMAL  LOCOMOTION. 

the  horizon,1  rotates  upon  its  anterior  margin  as  an  axis  during 
its  descent  and  causes  its  under  surface  to  make  a  gradually 
increasing  angle  with  the  horizon,  the  posterior  margin  (fig. 
53,  c)  in  this  movement  descending  beneath  the  anterior 
one.  A  similar  but  opposite  rotation  takes  place  during  the 
up  stroke.  The  rotation  referred  to  causes  the  wing  to  twist 
on  its  long  axis  screw-fashion,  and  to  describe  a  figure-of-8 
track  in  space,  one-half  of  the  figure  being  described  during 
the  ascent  of  the  wing,  the  other  half  during  its  descent. 
The  twisting  of  the  wing  and  the  figure-of-8  track  described 
by  it  when  made  to  vibrate,  are  represented  at  fig.  53. 
The  rotation  of  the  wing  on  its  long  axis  as  it  ascends  and 
descends  causes  the  under  surface  of  the  wing  to  act  as  a 
kite,  both  during  the  up  and  down  strokes,  provided  always 
the  body  bearing  the  wing  is  in  forward  motion.  But  the 
upper  surface  of  the  wing,  as  has  been  explained,  acts  when 
the  wing  is  being  elevated,  so  that  both  the  upper  and  under 
surfaces  of  the  wing  are  efficient  during  the  up  stroke.  When 
the  wing  ascends,  the  upper  surface  impinges  against  the  air; 
the  under  surface  impinging  at  the  same  time  from  its  being 
carried  obliquely  forward,  after  the  manner  of  a  kite,  by  the 
body,  which  is  in  motion.  During  the  down  stroke,  the 
under  surface  only  acts.  The  wing  is  consequently  effective 
both  during  its  ascent  and  descent,  its  slip  being  nominal  in 
amount.  The  wing  acts  as  a  kite,  both  when  it  ascends  and 
descends.  It  acts  more  as  a  propeller  than  an  elevator  during 
its  ascent ;  and  more  as  an  elevator  than  a  propeller  during 
its  descent.  It  is,  however,  effective  both  in  an  upward  and 
downward  direction.  The  efficiency  of  the  wing  is  greatly  in- 
creased by  the  fact  that  when  it  ascends  it  draws  a  current  of 
air  up  after  it,  which  current  being  met  by  the  wing  during 
its  descent,  greatly  augments  the  power  of  the  down  stroke. 
In  like  manner,  when  the  wing  descends  it  draws  a  current 
of  air  down  after  it,  which  being  met  by  the  wing  during  its 
ascent,  greatly  augments  the  power  of  the  up  stroke.  These 
induced  currents  are  to  the  wing  what  a  stiff  autumn  breeze  is 
to  the  boy's  kite.  The  wing  is  endowed  with  this  very  re- 

1  In  some  cases  the  posterior  margin  is  slightly  elevated  above  the  horizon 
(fig.  53,  <7). 


PROGRESSION  IN  OR  THROUGH  THE  AIR. 


107 


markable  property,  that  it  creates  the  current  on  which  it  rises 
and  progresses.  It  literally  flies  on  a  whirlwind  of  its  own 
forming. 

These  remarks  apply  more  especially  to  the  wings  of  bats 
and  birds,  and  those  insects  whose  wings  are  made  to  vibrate 
in  a  more  or  less  vertical  direction.  The  action  of  the  wing 
is  readily  imitated,  as  a  reference  to  fig.  53  will  show. 


Fio.  53. 

If,  for  example,  I  take  a  tapering  elastic  reed,  as  represented 
at  a  b,  and  supply  it  with  a  flexible  elastic  sail  (c  d),  and  a 
ball-and-socket  joint  (x),  I  have  only  to  seize  the  reed  at  a 
and  cause  it  to  oscillate  upon  x  to  elicit  all  the  wing  move- 
ments. By  depressing  the  root  of  the  reed  in  the  direction 
n  e,  the  wing  flies  up  as  a  kite  in  the  direction  j  f.  During 
the  upward  movement  the  wing  flies  upwards  and  forwards, 
and  describes  a  double  curve.  By  elevating  the  root  of  the 
reed  in  the  direction  m  a,  the  wing  flies  down  as  a  kite  in 
the  direction  i  b.  During  the  downward  movement  the 
wing  flies  downwards  and  forwards,  and  describes  a  double 
curve.  These  curves,  when  united,  form  a  waved  track, 
which  represents  progressive  flight.  During  the  rise  and  fall 
of  the  wing  a  large  amount  of  tractile  force  is  evolved,  and 
if  the  wings  and  the  body  of  the  flying  creature  are  inclined 
slightly  upwards,  kite-fashion,  as  they  invariably  are  in  ordi- 
nary flight,  the  whole  mass  of  necessity  moves  upwards  and 


104  ANIMAL  LOCOMOTION. 

necessary  degree  of  resistance  and  non-resistance.  Although 
the  third  order  of  lever  is  particularly  inefficient  when  the 
fulcrum  is  rigid  and  immobile,  it  possesses  singular  advantages 
when  these  conditions  are  reversed,  i.e.  when  the  fulcrum,  as 
happens  with  the  air,  is  elastic  and  yielding.  In  this  case  a 
very  slight  movement  at  the  root  of  the  pinion,  or  that  end 
of  the  lever  directed  towards  the  body,  is  succeeded  by  an 
immense  sweep  of  the  extremity  of  the  wing,  where  its  elevat- 
ing and  propelling  power  is  greatest.  This  arrangement  in- 
sures that  the  large  quantity  of  air  necessary  for  propulsion 
and  support  shall  be  compressed  under  the  most  favourable 
conditions. 

It  follows  from  this  that  those  insects  and  birds  are  endowed 
with  the  greatest  powers  of  flight  whose  wings  are  the  longest. 
The  dragon-fly  and  albatross  furnish  examples.  The  former 
on  some  occasions  dashes  along  with  amazing  velocity  and 
wheels  with  incredible  rapidity ;  at  other  times  it  suddenly 
checks  its  headlong  career  and  hovers  or  fixes  itself  in  the  air 
after  the  manner  of  the  kestrel  and  humming-birds.  The  flight 
of  the  albatross  is  also  remarkable.  This  magnificent  bird,  I  am 
infonned  on  reliable  authority,  sails  about  with  apparent  un- 
concern for  hours  together,  and  rarely  deigns  to  flap  its  enor- 
mous pinions,  which  stream  from  its  body  like  ribbons  to  the 
extent,  in  some  cases,  of  seven  feet  on  either  side. 

The  manner  in  which  the  wing  levers  the  body  upwards 
and  forwards  in  flight  is  shown  at  fig.  52. 

In  this  fig.  //'  represent  the  moveable  fulcra  furnished  by 
the  air ;  p  p'  the  power  residing  in  the  wing,  and  b  the  body 
to  be  flown.  In  order  to  make  the  problem  of  flight  more 
intelligible,  I  have  prolonged  the  lever  formed  by  the  wing 
beyond  the  body  (b),  and  have  applied  to  the  root  of  the  wing 
so  extended  the  weight  w  w'.  x  represents  the  universal 
joint  by  which  the  wing  is  attached  to  the  body.  When  the 
wing  ascends,  as  shown  zip,  the  air  (=  fulcrum/)  resists  its 
upward  passage,  and  forces  the  body  (b),  or  its  representative 
(w),  slightly  downwards.  When  the  wing  descends,  as  shown 
at  p',  the  air  (=  fulcrum  /')  resists  its  downward  passage, 
and  forces  the  body  (b),  or  its  representative  (w'},  slightly 
upwards.  From  this  it  follows,  that  when  the  wing  rises  the 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  105 

body  falls,  and  vice  versd',  the  wing  describing  the  arc  of  a 
large  circle  (//'),  the  body  (b),  or  the  weights  representing  it 
(w  w')  describing  the  arc  of  a  much  smaller  circle.  The  body, 


w 


b 


FIG.  52. 


therefore,  as  well  as  the  wing,  rises  and  falls  in  flight.  When 
the  wing  descends  it  elevates  the  body,  the  wing  being  active 
and  the  body  passive ;  when  the  body  descends  it  elevates 
the  wing,  the  body  being  active  and  the  wing  passive.  The 
elevator  muscles,  and  the  reaction  of  the  air  on  the  under 
surface  of  the  wing,  contribute  to  its  elevation.  It  is  in  this 
manner  that  weight  forms  a  factor  in  flight,  the  wing  and  the 
weight  of  the  body  reciprocating  and  mutually  assisting  and 
relieving  each  other.  This  is  an  argument  for  employing 
four  wings  in  artificial  flight,  the  wings  being  so  arrranged 
that  the  two  which  are  up  shall  always  by  their  fall  mechani- 
cally elevate  the  two  which  are  down.  Such  an  arrangement 
is  calculated  greatly  to  conserve  the  driving  power,  and,  as  a 
consequence,  to  reduce  the  weight.  It  is  the  upper  or  dorsal 
surface  of  the  wing  which  more  especially  operates  upon  the 
air  during  the  up  stroke,  and  the  under  or  ventral  surface 
which  operates  during  the  down  stroke.  The  wing,  which  at 
the  beginning  of  the  down  stroke  has  its  surfaces  and  margins 
(anterior  and  posterior)  arranged  in  nearly  the  same  plane  with 
6 


108 


ANIMAL  LOCOMOTION. 


forwards.  To  this  there  is  no  exception.  A  sheet  of  paper 
or  a  card  will  float  along  if  its  anterior  margin  is  slightly 
raised,  and  if  it  be  projected  with  sufficient  velocity.  The 
wings  of  all  flying  creatures  when  made  to  vibrate,  twist  and 
untwist,  the  posterior  thin  margin  of  each  wing  twisting 
round  the  anterior  thick  one,  like  the  blade  of  a  screw.  The 
artificial  wing  represented  at  fig.  53  (p.  107)  does  the  same,  cd 
twisting  round  a  b,  and  g  h  round  e  f.  The  natural  and  arti- 
ficial wings,  when  elevated  and  depressed,  describe  a  figure-of-8 
track  in  space  when  the  bodies  to  which  they  are  attached 
are  stationary.  When  the  bodies  advance,  the  figure-of-8  is 
opened  out  to  form  first  a  looped  and  then  a  waved  track.  I 
have  shown  how  those  insects,  bats,  and  birds  which  flap 
their  wings  in  a  more  or  less  vertical  direction  evolve  tractile 
or  propelling  power,  and  how  this,  operating  on  properly 
constructed  inclined  surfaces,  results  in  flight.  I  wish  now 
to  show  that  flight  may  also  be  produced  by  a  very  oblique 
and  almost  horizontal  stroke  of  the  wing,  as  in  some  insects, 
e.g.  the  wasp,  blue-bottle,  and  other  flies.  In  those  insects 
the  wing  is  made  to  vibrate  with  a  figure-of-8  sculling 


FIG.  54. 


motion  in  a  very  oblique  direction,  and  with  immense  energy. 
This  form  of  flight  differs  in  no  respect  from  the  other,  unless 
in  the  direction  of  the  stroke,  and  can  be  readily  imitated,  as 
a  reference  to  fig.  54  will  show. 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  109 

In  this  figure  (5  4)  the  conditions  represented  at  fig.  5  3  (p. 
107)  are  exactly  reproduced,  the  only  difference  being  that  in 
the  present  figure  the  wing  is  applied  to  the  air  in  a  more  or  less 
horizontal  direction,  whereas  in  fig.  53  it  is  applied  in  a  more 
or  less  vertical  direction.  The  letters  in  both  figures  are  the 
same.  The  insects  whose  wings  tack  upon  the  air  in  a  more 
or  less  horizontal  direction,  have  an  extensive  range,  each 
wing  describing  nearly  half  a  circle,  these  half  circles  corre- 
sponding to  the  area  of  support.  The  body  of  the  insect  is 
consequently  the  centre  of  a  circle  of  motion.  It  corresponds 
to  x  of  the  present  figure  (fig.  5  4).  When  the  wing  is  seized 
by  the  hand  at  a,  and  the  root  made  to  travel  in  the  direction 
n  e,  the  body  of  the  wing  travels  in  the  direction  j  f.  While 
so  travelling,  it  flies  upwards  in  a  double  curve,  kite-fashion, 
and  elevates  the  weight  I.  When  it  reaches  the  point  /,  it 
reverses  suddenly  to  prepare  for  a  return  stroke,  which  is 
produced  by  causing  the  root  of  the  wing  to  travel  in  the 
direction  m  a,  the  body  and  tip  travelling  in  the  direction  i  b. 
During  the  reverse  stroke,  the  wing  flies  upwards  in  a  double 
curve,  kite-fashion,  and  elevates  the  weight  k.  The  more 
rapidly  these  movements  are  repeated,  the  more  powerful  the 
wing  becomes,  and  the  greater  the  weight  it  elevates.  This 
follows  because  of  the  reciprocating  action  of  the  wing, — the 
wing,  as  already  explained,  always  drawing  a  current  of  air 
after  it  during  the  one  stroke,  which  is  met  and  utilized  by 
it  during  the  next  stroke.  The  reciprocating  action  of  the 
wing  here  referred  to  is  analogous  in  all  respects  to  that  ob- 
served in  the  flippers  of  the  seal,  sea-bear,  walrus,  and  turtle ; 
the  swimming  wing  of  the  penguin  ;  and  the  tail  of  the  whale, 
dugong,  manatee,  porpoise,  and  fish.  If  the  muscles  of  the 
insect  were  made  to  act  at  the  points  a  e,  the  body  of  the 
insect  would  be  elevated  as  at  k  I,  by  the  reciprocating  action 
of  the  wings.  The  amount  of  tractile  power  developed  in  the 
arrangement  represented  at  fig.  53  (p.  107),  can  be  readily 
ascertained  by  fixing  a  spring  or  a  weight  acting  over  a  pulley 
to  the  anterior  margin  (a  b  or  e  f)  of  the  wing ;  weights  acting 
over  pulleys  being  attached  to  the  root  of  the  wing  (a  or  e). 

The  amount  of  elevating  power  developed  in  the  arrange- 
ment  represented   at    fig.    54,   can    also    be   estimated    by 


110  ANIMAL  LOCOMOTION. 

causing  weights  acting  over  pulleys  to  operate  upon  the  root 
of  the  wing  (a  or  e),  and  watching  how  far  the  weights  (k  or  I) 
are  raised.  In  these  calculations  allowance  is  of  course  to  be 
made  for  friction.  The  object  of  the  two  sets  of  experiments 
described  and  figured,  is  to  show  that  the  wing  can  exert  a 
tractile  power  either  in  a  nearly  horizontal  direction  or  in  a 
nearly  vertical  one,  flight  being  produced  in  both  cases.  I 
wish  now  to  show  that  a  body  not  supplied  with  wings  or 
inclined  surfaces  will,  if  left  to  itself,  fall  vertically  down- 
wards ;  whereas,  if  it  be  furnished  with  wings,  its  vertical  fall 
is  converted  into  oblique  downward  flight.  These  are  very 
interesting  points.  Experiment  has  shown  me  that  a  wing 
when  made  to  vibrate  vertically  produces  horizontal  traction ; 
when  made  to  vibrate  horizontally,  vertical  traction;  the 
vertical  fall  of  a  body  armed  with  wings  producing  oblique 
traction.  The  descent  of  weights  can  also  be  made  to  propel 
the  wings  either  in  a  vertical  or  horizontal  direction;  the 
vibration  of  the  wings  upon  the  air  in  natural  flight  causing 
the  weights  (body  of  flying  creature)  to  move  forward. 
This  shows  the  very  important  part  performed  by  weight  in 
all  kinds  of  flight. 

Weight  necessary  to  Flight. — However  paradoxical  it  may 
seem,  a  certain  amount  of  weight  is  indispensable  in  flight. 

In  the  first  place,  it  gives  peculiar  efficacy  and  energy  to 
the  up  stroke,  by  acting  upon  the  inclined  planes  formed 
by  the  wings  in  the  direction  of  the  plane  of  progression. 
The  power  and  the  weight  may  thus  be  said  to  reciprocate, 
the  two  sitting,  as  it  were,  side  by  side,  and  blending  their 
peculiar  influences  to  produce  a  common  result. 

Secondly,  it  adds  momentum, — a  heavy  body,  when  once 
fairly  under  weigh,  meeting  with  little  resistance  from  the 
air,  through  which  it  sweeps  like  a  heavy  pendulum. 

Thirdly,  the  mere  act  of  rotating  the  wings  on  and  off 
the  wind  during  extension  and  flexion,  with  a  slight  down- 
word  stroke,  apparently  represents  the  entire  exertion  on  the 
part  of  the  volant  animal,  the  rest  being  performed  by  weight 
alone. 

This  last  circumstance  is  deserving  of  attention,  the  more 
especially  as  it  seems  to  constitute  the  principal  difference 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  Ill 

between  a  living  flying  thing  and  an  aerial  machine.  If  a 
flying-machine  was  constructed  in  accordance  with  the  prin- 
ciples which  we  behold  in  nature,  the  weight  and  the  pro- 
pelling power  of  the  machine  would  be  made  to  act  upon  the 
sustaining  and  propelling  surfaces,  whatever  shape  they 
assumed,  and  these  in  turn  would  be  made  to  operate  upon 
the  air,  and  vice  versd.  In  the  aerial  machine,  as  far  as  yet 
devised,  there  is  no  sympathy  between  the  weight  to  be 
elevated  and  the  lifting  power,  whilst  in  natural  flight  the  wings 
and  the  weight  of  the  flying  creature  act  in  concert  and  reci- 
procate ;  the  wings  elevating  the  body  the  one  instant,  the 
body  by  its  fall  elevating  the  wings  the  next.  When  the 
wings  elevate  the  body  they  are  active,  the  body  being  pas- 
sive. When  the  body  elevates  the  wings  it  is  active,  the 
wings  being  passive.  The  force  residing  in  the  wings,  and 
the  force  residing  in  the  body  (weight  is  a  force  when  launched 
in  space  and  free  to  fall  in  a  vertical  direction)  cause  the  mass 
of  the  volant  animal  to  oscillate  vertically  on  either  side  of 
an  imaginary  line — this  line  corresponding  to  the  path  of  the 
insect,  bat,  or  bird  in  the  air.  While  the  wings  and  body 
act  and  react  upon  each  other,  the  wings,  body,  and  air  like- 
wise act  and  react  upon  each  other.  In  the  flight  of  insects, 
bats,  and  birds,  weight  is  to  be  regarded  as  an  independent 
moving  power,  this  being  made  to  act  upon  the  oblique  sur- 
faces presented  by  the  wings  in  conjunction  with  the  power 
expended  by  the  animal — the  latter  being,  by  this  arrange- 
ment, conserved  to  a  remarkable  extent.  Weight,  assisted  by 
the  elastic  ligaments  or  springs,  which  recover  all  wings  in 
flexion,  is  to  be  regarded  as  the  mechanical  expedient  resorted 
to  by  nature  in  supplementing  the  efforts  of  all  flying  things.1 
Without  this,  flight  would  be  of  short  duration,  laboured,  and 
uncertain,  and  the  almost  miraculous  journeys  at  present  per- 
formed by  the  denizens  of  the  air  impossible. 

1  Weight,  as  is  well  known,  is  the  sole  moving  power  in  the  clock— the 
pendulum  being  used  merely  to  regulate  the  movements  produced  by  tlie 
descent  of  the  leads.  In  watches,  the  onus  of  motion  is  thrown  upon  a 
spiral  spring;  and  it  is  worthy  of  remark  that  the  mechanician  has  seized 
upon,  and  ingeniously  utilized,  two  forces  largely  employed  in  the  animal 
kingdom. 


112  ANIMAL  LOCOMOTION. 

PTeighl  contributes  to  Horizontal  Flight. — That  the  weight  of 
the  body  plays  an  important  part  in  the  production  of  flight 
may  be  proved  by  a  very  simple  experiment. 


FIG.  55. 

If  I  take  two  primary  feathers  and  fix  them  in  an  ordinary 
cork,  as  represented  at  fig.  55,  and  allow  the  apparatus  to 
drop  from  a  height,  I  find  the  cork  does  not  fall  vertically 
downwards,  but  downwards  and  forwards  in  a  curve.  This 
follows,  because  the  feathers  a,  b  are  twisted  flexible  inclined 
planes,  which  arch  in  an  upward  direction.  They  are  in  fact 
true  wings  in  the  sense  that  an  insect  wing  in  one  piece  is  a 
true  wing.  (Compare  a,  b,  c  of  fig.  55,  with  g,  g',  s  of  fig.  82, 
p.  158.)  When  dragged  downwards  by  the  cork  (c),  which 
would,  if  left  to  itself,  fall  vertically,  they  have  what  is  vir- 
tually a  down  stroke  communicated  to  them.  Under  these 
circumstances  a  struggle  ensues  between  the  cork  tending  to 
fall  vertically  and  the  feathers  tending  to  travel  in  an  upward 
direction,  and,  as  a  consequence,  the  apparatus  describes  the 
curve  d  e  f  g  before  reaching  the  earth  h,  i.  This  is  due  to 
the  action  and  reaction  of  the  feathers  and  air  upon  each 
other,  and  to  the  influence  which  gravity  exerts  upon  the 
cork.  The  forward  travel  of  the  cork  and  feathers,  as  com- 
pared with  the  space  through  which  they  fall,  is  very  great. 
Thus,  in  some  instances,  I  found  they  advanced  as  much  as  a 
yard  and  a  half  in  a  descent  of  three  yards.  Here,  then,  is 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  113 

an  example  of  flight  produced  by  purely  mechanical  appli- 
ances. The  winged  seeds  fly  in  precisely  the  same  manner. 
Thj6  seeds  of  the  plane-tree  have,  e.g.  two  wings  which 
exactly  resemble  the  wings  employed  for  flying ;  thus  they 
taper  from  the  root  towards  the  tip,  and  from  the  ante- 
rior margin  towards  the  posterior  margin,  the  margins  being 
twisted  and  disposed  in  different  planes  to  form  true  screws. 
This  arrangement  prevents  the  seed  from  falling  rapidly  or 
vertically,  and  if  a  breeze  is  blowing  it  is  wafted  to  a  con- 
siderable distance  before  it  reaches  the  ground.  Nature  is 
uniform  and  consistent  throughout.  She  employs  the  same 
principle,  and  very  nearly  the  same  means,  for  flying  a  heavy, 
solid  seed  which  she  employs  for  flying  an  insect,  a  bat,  or  a 
bird. 

When  artificial  wings  constructed  on  the  plan  of  natural 
ones,  with  stiff  roots,  tapering  semi-rigid  anterior  margins, 
and  thin  yielding  posterior  margins,  are  allowed  to  drop  from 
a  height,  they  describe  double  curves  in  falling,  the  roots  of 
the  wings  reaching  the  ground  first.  This  circumstance 
proves  the  greater  buoying  power  of  the  tips  of  the  wings  as 
compared  with  the  roots.  I  might  refer  to  many  other 
experiments  made  in  this  direction,  but  these  are  sufficient  to 
show  that  weight,  when  acting  upon  wings,  or,  what  is  the 
same  thing,  upon  elastic  twisted  inclined  planes,  must  be  re- 
garded as  an  independent  moving  power.  But  for  this  cir- 
cumstance flight  would  be  at  once  the  most  awkward  and 
laborious  form  of  locomotion,  whereas  in  reality  it  is  incom- 
parably the  easiest  and  most  graceful.  The  power  which 
rapidly  vibrating  wings  have  in  sustaining  a  body  which 
tends  to  fall  vertically  downwards,  is  much  greater  than  one 
would  naturally  imagine,  from  the  fact  that  the  body,  which 
is  always  beginning  to  fall,  is  never  permitted  actually  to  do 
so.  Thus,  when  it  has  fallen  sufficiently  far  to  assjst  in 
elevating  the  wings,  it  is  at  once  elevated  by  the  vigorous 
descent  of  those  organs.  The  body  consequently  never 
acquires  the  downward  momentum  which  it  would  do  if  per- 
mitted to  fall  through  a  considerable  space  uninterruptedly. 
It  is  easy  to  restrain  even  a  heavy  body  when  beginning  to 
fall,  while  it  is  next  to  impossible  to  check  its  progress  when 


114:  ANIMAL  LOCOMOTION. 

it  is  once  fairly  launched  in  space  and  travelling  rapidly  in  a 
downward  direction. 

Weight,  Momentum,  and  Power,  to  a  certain  extent,  synonymous 
in  Flight. — When  a  bird  rises  it  has  little  or  no  momentum,  so 
that  if  it  comes  in  contact  with  a  solid  resisting  surface  it 
does  not  injure  itself.  When,  however,  it  has  acquired  all 
the  momentum  of  which  it  is  capable,  and  is  in  full  and  rapid 
flight,  such  contact  results  in  destruction.  My  friend  Mr.  A. 
D.  Bartlett  informed  me  of  an  instance  where  a  wild  duck 
terminated  its  career  by  coming  violently  in  contact  with  one 
of  the  glasses  of  the  Eddystone  Lighthouse.  The  glass,  which 
was  fully  an  inch  in  thickness,  was  completely  smashed. 
Advantage  is  taken  of  this  circumstance  in  killing  sea-birds, 
a  bait  being  placed  on  a  board  and  set  afloat  with  a  view  to 
breaking  the  ne«,k  of  the  bird  when  it  stoops  to  seize  the  car- 
rion. The  additional  power  due  to  momentum  in  heavy 
bodies  in  motion  is  well  illustrated  in  the  start  and  progress 
of  steamboats.  In  these  the  slip,  as  it  is  technically  called, 
decreases  as  the  speed  of  the  vessel  increases ;  the  strength  of 
a  man,  if  applied  by  a  hawser  attached  to  the  stern  of  a 
moderate-sized  vessel,  being  sufficient  to  retard,  and,  in  some 
instances  prevent,  its  starting.  In  such  a  case  the  power  of  the 
engine  is  almost  entirely  devoted  to  "  slip  "  or  in  giving  motion 
to  the  fluid  in  which  the  screw  or  paddle  is  immersed.  It  is 
consequently  not  the  power  residing  in  the  paddle  or  screw 
which  is  cumulative,  but  the  momentum  inhering  in  the  mass. 
In  the  bird,  the  momentum,  alias  weight,  is  made  to  act  upon 
the  inclined  planes  formed  by  the  wings,  these  adroitly  con- 
verting it  into  sustaining  and  propelling  power.  It  is  to  this 
circumstance,  more  than  any  other,  that  the  prolonged  flight 
of  birds  is  mainly  due,  the  inertia  or  dead  weight  of  the 
trunk  aiding  and  abetting  the  action  of  the  wings,  and  so 
relieving  the  excess  of  exertion  which  would  necessarily 
devolve  on  the  bird.  It  is  thus  that  the  power  which  in 
living  structures  resides  in  the  mass  is  conserved,  and  the 
mass  itself  turned  to  account.  But  for  this  reciprocity,  no 
bird  could  retain  its  position  in  the  air  for  more  than  a  few 
minutes  at  a  time.  This  is  proved  by  the  comparatively 
brief  upward  flight  of  the  lark  and  the  hovering  of  the  hawk 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  115 

when  hunting.  In  both  these  cases  the  body  is  exclusively 
sustained  by  the  action  of  the  wings,  the  weight  of  the  trunk 
taking  no  part  in  it ;  in  other  words,  the  weight  of  the  body 
does  not  contribute  to  flight  by  adding  its  momentum  and 
the  impulse  which  momentum  begets.  In  the  flight  of  the 
albatross,  on  the  other  hand,  the  momentum  acquired  by  the 
moving  mass  does  the  principal  portion  of  the  work,  the  wings 
for  the  most  part  being  simply  rotated  on  and  off  the  wind  to 
supply  the  proper  angles  necessary  for  the  inertia  or  mass  to 
operate  upon.  It  appears  to  me  that  in  this  blending  of 
active  and  passive  power  the  mystery  of  flight  is  concealed, 
and  that  no  arrangement  will  succeed  in  producing  flight 
artificially  which  does  not  recognise  and  apply  the  principle 
here  pointed  out. 

Air-cells  in  Insects  and  Birds  not  necessary  to  Flight. — The 
boasted  levity  of  insects,  bats,  and  birds,  concerning  which  so 
much  has  been  written  by  authors  in  their  attempts  to  explain 
flight,  is  delusive  in  the  highest  degree. 

Insects,  bats,  and  birds  are  as  heavy,  bulk  for  bulk,  as  most 
other  living  creatures,  and  flight  can  be  performed  perfectly 
by  animals  which  have  neither  air-sacs  nor  hollow  bones  ;  air- 
sacs  being  found  in  animals  never  designed  to  fly.  Those 
who  subscribe  to  the  heated-air  theory  are  of  opinion  that  the 
air  contained  in  the  cavities  of  insects  and  birds  is  so  much 
lighter  than  the  surrounding  atmosphere,  that  it  must  of 
necessity  contribute  materially  to  flight.  I  may  mention, 
however,  that  the  quantity  of  air  imprisoned  is,  to  begin 
with,  so  infinitesimally  small,  and  the  difference  in  weight 
which  it  experiences  by  increase  of  temperature  so  inappre- 
ciable, that  it  ought  not  to  be  taken  into  account  by  any  one 
endeavouring  to  solve  the  difficult  and  important  problem  of 
flight.  The  Montgolfier  or  fire-balloons  were  constructed  on 
the  heated-air  principle  ;  but  as  these  have  no  analogue  in 
nature,  and  are  apparently  incapable  of  improvement,  they 
are  mentioned  here  rather  to  expose  what  I  regard  a  false 
theory  than  as  tending  to  elucidate  the  true  principles  of 
flight. 

When  we  have  said  that  cylinders  and  hollow  chambers 
increase  the  area  of  the  insect  and  bird,  and  that  an  insect 


116  ANIMAL  LOCOMOTION. 

and  bird  so  constructed  is  stronger,  weight  for  weight,  than 
one  composed  of  solid  matter,  we  may  dismiss  the  subject ; 
flight  being,  as  I  shall  endeavour  to  show  by-and-by,  not  so 
much  a  question  of  levity  as  one  of  weight  and  power  intelli- 
gently directed,  upon  properly  constructed  flying  surfaces. 

The  bodies  of  insects,  bats,  and  birds  are  constructed  on 
strictly  mechanical  principles, — lightness,  strength,  and  dura- 
bility of  frame  being  combined  with  power,  rapidity,  and 
precision  of  action.  The  cylindrical  method  of  construction 
is  in  them  carried  to  an  extreme,  the  bodies  and  legs  of 
insects  displaying  numerous  unoccupied  spaces,  while  the 
muscles  and  solid  parts  are  tunnelled  by  innumerable  air- 
tubes,  which  communicate  with  the  surrounding  medium  by 
a  series  of  apertures  termed  spiracles. 

A  somewhat  similar  disposition  of  parts  is  met  with  in 
birds,  these  being  in  many  cases  furnished  not  only  with 
hollow  bones,  but  also  (especially  the  aquatic  ones)  with  a 
liberal  supply  of  air-sacs.  They  are  likewise  provided  with  a 
dense  covering  of  feathers  or  down,  which  adds  greatly  to 
their  bulk  without  materially  increasing  their  weight.  Their 
bodies,  moreover,  in  not  a  few  instances,  particularly  in  birds 
of  prey,  are  more  or  less  flattened.  The  air-sacs  are  well 
seen  in  the  swan,  goose,  and  duck ;  and  I  have  on  several 
occasions  minutely  examined  them  with  a  view  to  determine 
their  extent  and  function.  In  two  of  the  specimens  which  I 
injected,  the  material  employed  had  found  its  way  not  only 
into  those  usually  described,  but  also  into  others  which  ramify 
in  the  substance  of  the  muscles,  particularly  the  pectorals. 
No  satisfactory  explanation  of  the  purpose  served  by  these 
air-sacs  has,  I  regret  to  say,  been  yet  tendered.  According 
to  Sappey,1  who  has  devoted  a  large  share  of  attention  to  the 
subject,  they  consist  of  a  membrane  which  is  neither  serous 
nor  mucous,  but  partly  the  one  and  partly  the  other ;  and  as 
blood-vessels  in  considerable  numbers,  as  my  preparations 

1  Sappey  enumerates  fifteen  air- sacs, — the  thoracic,  situated  at  the  lower 
part  of  the  neck,  behind  the  sternum  ;  two  cervical,  which  run  the  whole 
length  of  the  neck  to  the  head,  which  they  supply  with  -air ;  two  pairs  of 
anterior,  and  two  pairs  of  posterior  diaphragmatic  ;  and  two  pairs  of  abdo- 
minal. 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  117 

show,  ramify  in  their  substance,  and  they  are  in  many  cases 
covered  with  muscular  fibres  which  confer  on  them  a  rhythmic 
movement,  some  recent  observers  (Mr.  Drosier l  of  Cambridge, 
for  example)  have  endeavoured  to  prove  that  they  are  ad- 
juncts of  the  lungs,  and  therefore  assist  in  aerating  the  blood. 
This  opinion  was  advocated  by  John  Hunter  as  early  as 
1774,2  and  is  probably  correct,  since  the  temperature  of  birds 
is  higher  than  that  of  any  other  class  of  animals,  and  because 
they  are  obliged  occasionally  to  make  great  muscular  exer- 
tions both  in  swimming  and  flying.  Others  have  viewed  the 
air-sacs  in  connexion  with  the  hollow  bones  frequently,  though 
not  always,  found  in  birds,3  and  have  come  to  look  upon  the 
heated  air  which  they  contain  as  being  more  or  less  essential 
to  flight.  That  the  air-cells  have  absolutely  nothing  to  do  with 
flight  is  proved  by  the  fact  that  some  excellent  fliers  (take  the 
bats,  e.g.)  are  destitute  of  them,  while  birds  such  as  the 
ostrich  and  apteryx,  which  are  incapable  of  flying,  are  pro- 
vided with  them.  Analogous  air-sacs,  moreover,  are  met 
with  in  animals  never  intended  to  fly;  and  of  these  I  may 
instance  the  great  air-sac  occupying  the  cervical  and  axil- 
lary regions  of  the  orang-outang,  the  float  or  swimming- 
bladder  in  fishes,  and  the  pouch  communicating  with  the 
trachea  of  the  emu.4 

1  "  On  the  Functions  of  the  Air-cells  .and  the  Mechanism  of  Respiration  in 
Birds,"  by  W.  H.  Drosier,  M.D.,  Caius  College.— Proc.  Camb.  Phil.  Soc., 
Feb.  12, 1866. 

2  "  An  Account  of  certain  Receptacles  of  Air  in  Birds  which  communicate 
with  the  Lungs,  and  are  lodged  among  the  Fleshy  Parts  and  in  the  Hollow 
Bones  of  these  Animals." — Phil.  Trans.,  Lond.  1774. 

3  According  to  Dr.  Crisp  the  swallow,  martin,  snipe,  and  many  birds  of 
passage  have  no  air  in  their  bones  (Proc.  Zool.  Soc.,  Lond.  part  xxv.  1857,  p. 
13).    The  same  author,  in  a  second  communication  (pp.  215  and  216),  adds 
that  the  glossy  starling,  spotted  flycatcher,  whin- chat,  wood-wren,  willow-wren, 
black-headed  bunting,  and  canary,  five  of  which  are  birds  of  passage,  have 
likewise  no  air  in  their  bones.     The  following  is  Dr.  Crisp's  summary  :— Out 
of  ninety-two  birds  examined  he  found   "  air  in  many  of  the  bones,  five 
(Falconidos) ;  air  in  the  humeri  and  not  in  the  inferior  extremities,  thirty- 
nine  ;  no  air  in  the  extremities  and  probably  none  in  the  other  bones,  forty- 
eight," 

4  Nearly  allied  to  this  is  the  great  gular  pouch  of  the  bustard.     Specimens 
of  the  air-sac  in  the  orang,  emu,  and  bustard,  and  likewise  of  the  air-sacs  of 


1 1 8  ANIMAL  LOCOMOTION. 

The  same  may  be  said  of  the  hollow  bones, — some  really 
admirable  fliers,  as  the  swifts,  martins,  and  snipes,  having 
their  bones  filled  with  marrow,  while  those  of  the  wingless 
running  birds  alluded  to  have  air.  Furthermore  and  finally, 
a  living  bird  weighing  10  Ibs.  weighs  the  same  when  dead, 
plus  a  very  few  grains  ;  and  all  know  what  effect  a  few  grains 
of  heated  air  would  have  in  raising  a  weight  of  10  Ibs.  from 
the  ground. 

How  Balancing  is  effected  in  Flight,  the  Sound  produced  by 
the  Wing,  etc. — The  manner  in  which  insects,  bats,  and  birds 
balance  themselves  in  the  air  has  hitherto,  and  with  reason, 
been  regarded  a  mystery,  for  it  is  difficult  to  understand  how 
they  maintain  their  equilibrium  when  the  wings  are  beneath 
their  bodies.  Figs.  67  and  68,  p.  141,  throw  considerable 
light  on  the  subject  in  the  case  of  the  insect.  In  those 
figures  the  space  (a,  g)  mapped  out  by  the  wing  during  its 
vibrations  is  entirely  occupied  by  it ;  i.e.  the  wing  (such  is 
its  speed)  is  in  every  portion  of  the  space  at  nearly  the  same 
instant,  the  space  representing  what  is  practically  a  solid 
basis  of  support.  As,  moreover,  the  wing  is  jointed  to  the 
upper  part  of  the  body  (thorax)  by  a  universal  joint,  which 
admits  of  every  variety  of  motion,  the  insect  is  always  sus- 
pended (very  much  as  a  compass  set  upon  gimbals  is  sus- 
pended) ;  the  wings,  when  on  a  level  with  the  body,  vibrating 
in  such  a  manner  as  to  occupy  a  circular  area  (vide  r dbf  of 
fig.  56,  p.  120),  in  the  centre  of  which  the  body  (a,  e  c)  is 
placed.  The  wings,  when  vibrating  above  and  beneath  the 
body  occupy  a  conical  area ;  the  apex  of  the  cone  being  directed 
upwards  when  the  wings  are  below  the  body,  and  downwards 
when  they  are  above  the  body.  Those  points  are  well  seen 
in  the  bird  at  figs.  82  and  83,  p.  158.  In  fig.  82  the  in- 
verted cone  formed  by  the  wings  when  above  the  body  is  repre- 
sented, and  in  fig.  83  that  formed  by  the  wings  when  below 
the  body  is  given.  In  these  figures  it  will  be  observed  that 
the  body,  from  the  insertion  of  the  roots  of  the  wings  into  its 
upper  portion,  is  always  suspended,  and  this,  of  course,  is  equi- 
valent to  suspending  the  centre  of  gravity.  In  the  bird  and 

the  swan  and  goose,  as  prepared  by  me,  may  be  seen  in  the  Museum  of  the 
Royal  College  of  Surgeons  of  England. 


PROGRESSION  IN  OK  THROUGH  THE  AIR.      119 

bat,  where  the  stroke  is  delivered  more  vertically  than  in  the 
insect,  the  basis  of  support  is  increased  by  the  tip  of  the  wing 
folding  inwards  and  backwards  in  a  more  or  less  horizontal 
direction  at  the  end  of  the  down  stroke  ;  and  outwards  and 
forwards  at  the  end  of  the  up  stroke.  This  is  accompanied 
by  the  rotation  of  the  outer  portion  of  the  wing  upon  the 
w  rist  as  a  centre,  the  tip  of  the  wing,  because  of  the  ever 
varying  position  of  the  wrist,  describing  an  ellipse.  In  in- 
sects whose  wings  are  broad  and  large  (butterfly),  and  which 
are  driven  at  a  comparatively  low  speed,  the  balancing  power 
is  diminished.  In  insects  whose  wings,  on  the  contrary,  are 
long  and  narrow  (blow-fly),  and  which  are  driven  at  a  high 
speed,  the  balancing  power  is  increased.  It  is  the  same  with 
short  and  long  winged  birds,  so  that  the  function  of  balancing 
is  in  some  measure  due  to  the  form  of  the  wing,  and  the 
speed  with  which  it  is  driven  ;  the  long  wing  and  the  wing 
vibrated  with  great  energy  increasing  the  capacity  for  balanc- 
ing. When  the  body  is  light  and  the  wings  very  ample 
(butterfly  and  heron),  the  reaction  elicited  by  the  ascent 
and  descent  of  the  wing  displaces  the  body  to  a  marked 
extent.  When,  on  the  other  hand,  the  wings  are  small 
and  the  body  large,  the  reaction  produced  by  the  vibration 
of  the  wing  is  scarcely  perceptible.  Apart,  however,  from 
the  shape  and  dimensions  of  the  wing,  and  the  rapidity 
with  which  it  is  urged,  it  must  never  be  overlooked  that  all 
wings  (as  has  been  pointed  out)  are  attached  to  the  bodies 
of  the  animals  bearing  them  by  some  form  of  universal 
joint,  and  in  such  a  manner  that  the  bodies,  whatever  the 
position  of  the  wings,  are  accurately  balanced,  and  swim 
about  in  a  more  or  less  horizontal  position,  like  a  compass  set 
upon  gimbals.  To  such  an  extent  is  this  true,  that  the  posi- 
tion of  the  wing  is  a  matter  of  indifference.  Thus  the  pinion 
may  be  above,  beneath,  or  on  a  level  with  the  body ;  or  it 
may  be  directed  forwards,  backwards,  or  at  right  angles  to 
the  body.  In  either  case  the  body  is  balanced  mechanically 
and  without  effort.  To  prove  this  point  I  made  an  artificial 
wing  and  body,  and  united  the  one  to  the  other  by  a  uni- 
versal joint.  I  found,  as  I  had  anticipated,  that  in  whatever 
position  the  wing  was  placed,  whether  above,  beneath,  or  on 


120 


ANIMAL  LOCOMOTION. 


a  level  with  the  body,  or  on  either  side  of  it,  the  body  almost 
instantly  attained  a  position  of  rest.  The  body  was,  in  fact, 
equally  suspended  and  balanced  from  all  points. 

Rapidity  of  Wing  Movements  partly  accounted  for. — Much 
surprise  has  been  expressed  at  the  enormous  rapidity  with 
which  some  wings  are  made  to  vibrate.  The  wing  of  the 
insect  is,  as  a  rule,  very  long  and  narrow.  As  a  consequence, 
a  comparatively  slow  and  very  limited  movement  at  the  root 


Fig.  56.1 

confers  great  range  and  immense  speed  at  the  tip ;  the  speed 
of  each  portion  of  the  wing  increasing  as  the  root  of  the  wing 
is  receded  from.  This  is  explained  on  a  principle  well  under- 
stood in  mechanics,  viz.  that  when  a  rod  hinged  at  one  end 
is  made  to  move  in  a  circle,  the  tip  or  free  end  of  the  rod 
describes  a  much  wider  circle  in-  a  given  time  than  a  portion 
of  the  rod  nearer  the  hinge.  This  principle  is  illustrated  at 
1  In  this  diagram  I  have  purposely  represented  the  right  wing  by  a  straight 
rigid  rod.  The  natural  wing,  however,  is  curved,  flexible,  and  elastic.  It 
likewise  moves  In  curves,  the  curves  being  most  marked  towards  the  end  of 
the  up  and  down  strokes,  •  as  shown  at  m  n,  o  p.  The  curves,  which  are 
double  flgure-of-8  curves,  are  obliterated  towards  the  middle  of  the  strokes  (a  r). 
This  remark  holds  true  of  all  natural  wings,  and  of  all  artificial  wings  properly 
constructed.  The  curves  and  the  reversal  thereof  are  necessary  to  give  con- 
tinuity of  motion  to  the  wing  during  its  vibrations,  and  what  is  not  less 
important,  to  enable  the  wing  alternately  to  seize  and  dismiss  the  air. 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  121 

fig.  56.  Thus  if  a  &  of  fig.  56  be  made  to  represent  the 
rod  hinged  at  x,  it  travels  through  the  space  d  bf  in  the 
same  time  it  travels  through  j  k  I  •;  and  through  j  k  I  in  the 
same  time  it  travels  through  g  h  i  ;  and  through  ghiin  the 
same  time  it  travels  through  e  a  c,  which  is  the  area  occupied 
by  the  thorax  of  the  insect.  If,  however,  the  part  of  the  rod 
b  travels  through  the  space  d  bfin  the  same  time  that  the  part 
a  travels  through  the  space  e  a  c,  it  follows  of  necessity  that 
the  portion  of  the  rod  marked  a  moves  very  much  slower 
than  that  marked  b.  The  muscles  of  the  insect  are  applied 
at  the  point  a,  as  short  levers  (the  point  referred  to  correspond- 
ing to  the  thorax  of  the  insect),  so  that  a  comparatively  slow 
and  limited  movement  at  the  root  of  the  wing  produces  the 
marvellous  speed  observed  at  the  tip  ;  the  tip  and  body  of  the 
wing  being  those  portions  which  occasion  the  blur  or  impres- 
sion produced  on  the  eye  by  the  rapidly  oscillating  pinion  (figs. 
64,  65,  and  66,  p.  139),  But  for  this  mode  of  augmenting 
the  speed  originally  inaugurated  by  the  muscular  system,  it  is 
difficult  to  comprehend  how  the  wings  could  be  driven  at  the 
velocity  attributed  to  them.  The  wing  of  the  blow-fly  is 
said  to  make  300  strokes  per  second,  i.e.  18,000  per  minute. 
Now  it  appears  to  me  that  muscles  to  contract  at  the  rate  of 
18,000  times  in  the  minute  would  be  exhausted  in  a  very 
few  seconds,  a  state  of  matters  which  would  render  the  con- 
tinuous flight  of  insects  impossible.  (The  heart  contracts  only 
between  sixty  and  seventy  times  in  a  minute.)  I  am,  therefore, 
disposed  to  believe  that  the  number  of  contractions  made  by 
the  thoracic  muscles  of  insects  has  been  greatly  overstated; 
the  high  speed  at  which  the  wing  is  made  to  vibrate  being 
due  less  to  the  separate  and  sudden  contractions  of  the  muscles 
at  its  root  than  to  the  fact  that  the  speed  of  the  different 
parts  of  the  wing  is  increased  in  a  direct  ratio  as  the  several 
parts  are  removed  from  the  driving  point,  as  already  ex- 
plained. Speed  is  certainly  a  matter  of  great  importance 
in  wing  movements,  as  the  elevating  and  propelling  power  of 
the  pinion  depends  to  a  great  extent  upon  the  rapidity  with 
which  it  is  urged.  Speed,  however,  may  be  produced  in  two 
ways — either  by  a  series  of  separate  and  opposite  movements, 
such  as  is  witnessed  in  the  action  of  a  piston,  or  by  a  series 


122  ANIMAL  LOCOMOTION. 

of  separate  and  opposite  movements  acting  upon  an  instru- 
ment so  designed,  that  a  movement  applied  at  one  part  in- 
creases in  rapidity  as  the  point  of  contact  is  receded  from,  as 
happens  in  the  wing.  In  the  piston  movement  the  motion  is 
uniform,  or  nearly  so;  all  parts  of  the  piston  travelling  at 
very  much  the  same  speed.  In  the  wing  movements,  on  the 
contrary,  the  motion  is  gradually  accelerated  towards  the  tip 
of  the  pinion,  where  the  pinion  is  most  effective  as  an  elevator, 
and  decreased  towards  the  root,  where  it  is  least  effective — 
an  arrangement  calculated  to  reduce  the  number  of  muscular 
contractions,  while  it  contributes  to  the  actual  power  of  the 
wing.  This  hypothesis,  it  will  be  observed,  guarantees  to  the 
Aving  a  very  high  speed,  with  comparatively  few  reversals  and 
comparatively  few  muscular  contractions. 

In  the  bat  and  bird  the  wings  do  not  vibrate  with  the 
same  rapidity  as  in  the  insect,  and  this  is  accounted  for  by 
the  circumstance,  that  in  them  the  muscles  do  not  act  exclu- 
sively at  the  root  of  the  wing.  In  the  bat  and  bird  the 
muscles  run  along  the  wing  towards  the  tip  for  the  pur- 
pose of  flexing  or  folding  the  wing  prior  to  the  up  stroke, 
and  for  opening  out  and  expanding  it  prior  to  the  down 
stroke. 

As  the  wing  must  be  folded  or  flexed  and  opened  out  or 
expanded  every  time  the  wing  rises  and  falls,  and  as  the 
muscles  producing  flexion  and  extension  are  long  muscles 
with  long  tendons,  which  act  at  long  distances  as  long  levers, 
and  comparatively  slowly,  it  follows  that  the  great  short 
muscles  (pectorals,  etc.)  situated  at  the  root  of  the  wing  must 
act  slowly  likewise,  as  the  muscles  of  the  thorax  and  wing  of 
necessity  act  together  to  produce  one  pulsation  or  vibration 
of  the  wing.  What  the  wing  of  the  bat  and  bird  loses  in 
speed  it  gains  in  power,  the  muscles  of  the  bat  and  bird's 
wing  acting  directly  upon  the  points  to  be  moved,  and  under 
the  most  favourable  conditions.  In  the  insect,  on  the  con- 
trary, the  muscles  act  indirectly,  and  consequently  at  a  dis- 
advantage. If  the  pectorals  only  moved,  they  would  act  as 
short  levers,  and  confer  on  the  wing  of  the  bat  and  bird  the 
rapidity  peculiar  to  the  wing  of  the  insect. 

The  tones  emitted  by  the  bird's  wing  would  in  this  case 


PROGKESSION  IN  OR  THROUGH  THE  AIR.  123 

be  heightened.  The  swan  in  flying  produces  a  loud  whistling 
sound,  and  the  pheasant,  partridge,  and  grouse  a  sharp  whirring 
noise  like  the  stone  of  a  knife-grinder. 

It  is  a  mistake  to  suppose,  as  many  do,  that  the  tone  or 
note  produced  by  the  wing  during  its  vibrations  is  a  true 
indication  of  the  number  of  beats  made  by  it  in  any  given 
time.  This  will  be  at  once  understood  when  I  state,  that  a 
long  wing  will  produce  a  higher  note  than  a  shorter  one 
driven  at  the  same  speed  and  having  the  same  superficial 
area,  from  the  fact  that  the  tip  and  body  of  the  long  wing 
will  move  through  a  greater  space  in  a  given  time  than  the 
tip  and  body  of  the  shorter  wing.  This  is  occasioned  by  all 
wings  being  jointed  at  their  roots,  the  sweep  made  by  the 
different  parts  of  the  wing  in  a  given  time  being  longer  or 
shorter  in  proportion  to  the  length  of  the  pinion.  It  ought, 
moreover,  not  to  be  overlooked,  that  in  insects  the  notes  pro- 
duced are  not  always  referable  to  the  action  of  the  wings, 
these,  in  many  cases,  being  traceable  to  movements  induced 
in  the  legs  and  other  parts  of  the  body. 

It  is  a  curious  circumstance,  that  if  portions  be  removed 
from  the  posterior  margins  of  the  wings  of  a  buzzing  insect, 
such  as  the  wasp,  bee,  blue-bottle  fly,  etc.,  the  note  produced 
by  the  vibration  of  the  pinions  is  raised  in  pitch.  This  is 
explained  by  the  fact,  that  an  insect  whose  wings  are  curtailed 
requires  to  drive  them  at  a  much  higher  speed  in  order  to 
sustain  itself  in  the  air.  That  the  velocity  at  which  the  wing 
is  urged  is  instrumental  in  causing  the  sound,  is  proved  by 
the  fact,  that  in  slow-flying  insects  and  birds  no  note  is  pro- 
duced ;  whereas  in  those  which  urge  the  wing  at  a  high 
speed,  a  note  is  elicited  which  corresponds  within  certain 
limits  to  the  number  of  vibrations  and  the  form  of  the  wing. 
It  is  the  posterior  or  thin  flexible  margin  of  the  wing  which 
is  more  especially  engaged  in  producing  the  sound ;  and  if 
this  be  removed,  or  if  this  portion  of  the  wing,  as  is  the  case 
in  the  bat  and  owl,  be  constructed  of  very  soft  materials,  the 
character  of  the  note  is  altered.  An  artificial  wing,  if  pro- 
perly constructed  and  impelled  at  a  sufficiently  high  speed, 
emits  a  drumming  noise  which  closely  resembles  the  note 
produced  by  the  vibration  of  short-winged,  heavy-bodied 


124  ANIMAL  LOCOMOTION. 

birds,  all  which  goes  to  prove  that  sound  is  a  concomitant  of 
rapidly  vibrating  wings. 

The  Wing  area  Variable  and  in  Excess. — The  travelling- 
surfaces  of  insects,  bats,  and  birds  greatly  exceed  those  of 
fishes  and  swimming  animals ;  the  travelling-surfaces  of  swim- 
ming animals  being  greatly  in  excess  of  those  of  animals  which 
walk  and  run.  The  wing  area  of  insects,  bats,  and  birds 
varies  very  considerably,  flight  being  possible  within  a  com- 


Pio.  57.— Shows  a  butterfly  with  comparatively  very  large  wings.  The  nervures 
are  seen  to  great  advantage  in  this  specimen  :  and  the  enormous  expanse  of 
the  pinions  readily  explains  the  irregular  flight  of  the  insect  on  the  principle 
of  recoil,  a  Anterior  wing,  b  Posterior  wing,  e  Anterior  margin  of  wing. 
/Ditto  posterior  margin,  g  Ditto  outer  margin.  Compare  with  beetle,  fig. 
58.— Original. 

paratively  wide  range.  Thus  there  are  light-bodied  and  large- 
winged  insects  and  birds — as  the 'butterfly  (fig.  57)  and  heron 
(fig.  60,  p.  126)  ;  and  others  whose  bodies  are  comparatively 
heavy,  while  their  wings  are  insignificantly  small — as  the 
sphinx  moth  and  Goliath  beetle  (fig.  58)  among  insects,  and 
the  grebe,  quail,  and  partridge  (fig.  59,  p.  126)  among  birds. 
The  apparent  inconsistencies  in  the  dimensions  of  the  body 
and  wings  are  readily  explained  by  the  greater  musculardevelop- 
mcnt  of  the  heavy-bodied  short-winged  insects  and  birds,  and 
the  increased  power  and  rapidity  with  which  the  wings  in  them 
are  made  to  oscillate.  In  large-winged  animals  the  movements 


PROGRESSION  IN  OR  THROUGH  THE  AIR.       125 

are  slow;  in  small-winged  ones  comparatively  very  rapid.  This 
shows  that  flight  may  be  attained  by  a  heavy,  powerful 
animal  with  comparatively  small  wings,  as  well  as  by  a 
lighter  one  with  enormously  enlarged  Avings.  While  there  is 
apparently  no  fixed  relation  between  the  area  of  the  wings 
and  the  animal  to  be  raised,  there  is,  unless  in  the  case  of 
sailing  birds,1  an  unvarying  relation  between  the  weight  of 


Pio.  58. — Under-surface  of  large  beetle  (Goliathm  m,icans),  with  deeply  con- 
cave and  comparatively  small  wings  (compare  with  butterfly,  fig.  57),  showa 
that  the  nervurcs  (r,  d,  e,  f,  n,  u,  n)  of  the  wings  of  the  beetle  are  arranged 
along  the  anterior  margins  and  throughout  the  substance  of  the  wings 
generally,  very  much  as  the  bones  of  the  arm,  forearm,  and  hand,  are  in  the 
wings  of  the  bat,  to  which  they  bear  a  very  marked  resemblance,  both  in 
their  shape  and  mode  of  action.  The  wings  are  folded  upon  themselves  at 
the  point  e  during  repose.  Compare  letters  of  this  figure  with  similar  letters 
of  tig.  17,  p.  36.— Original. 

the  animal,  the  area  of  its  wings,  and  the  number  of  oscilla- 
tions made  by  them  in  a  given  time.  The  problem  of  flight 
thus  resolves  itself  into  one  of  weight,  power,  velocity,  and 
small  surfaces ;  versus  buoyancy,  debility,  diminished  speed, 

1  In  birds  which  skim,  sail,  or  glide,  the  pinion  is  greatly  elongated  or 
ribbon-shaped,  and  the  weight  of  the  body  is  made  to  operate  upon  the  in- 
clined planes  formed  by  the  wings,  in  such  a  manner  that  the  bird  when  it 
lias  once  got  fairly  under  weigh,  is  in  a  measure  self-supporting.  This  is 
especially  the  case  when  it  is  proceeding  against  a  slight  breeze — the  wind 
and  the  inclined  planes  resulting  from  the  upward  inclination  of  the  wings 
reacting  iipon  each  other,  with  this  very  remarkable  result,  that  the  mass  of 
the  bird  moves  steadily  forwards  in  a  more  or  less  horizontal  direction. 


12G 


ANIMAL  LOCOMOTION. 


and  extensive  surfaces, — weight  in  either  case  being  a  sine 
quA  non.  In  order  to  utilize  the  air  as  a  means  of  transit, 
the  body  in  motion,  whether  it  moves  in  virtue  of  the  life  it 
possesses,  or  because  of  a  force  superadded,  must  be  heavier 


FIG.  59. — The  Red-legged  Partridge  (Perdix  rubra)  with  wings  fully  extended 
as  in  rapid  flight,  shows  deeply  concave  form  of  the  wings,  how  the  primary 
and  secondary  feathers  overlap  and  support  each  other  during  extension, 
and  how  the  anterior  or  thick  margins  of  the  wings  are  directed  upwards 
and  forwards,  and  the  posterior  or  thin  ones  downwards  and  backwards. 
The  wings  in  the  partridge  are  wielded  with  immense  velocity  and  power. 
This  is  necessary  because  of  their  small  size  as  compared  with  the  great 
dimensions  and  weight  of  the  body. 

If  a  horizontal  line  be  drawn  across  the  feet  (a,  e]  to  represent  the  horizon, 
and  another  from  the  tip  of  the  tail  (a)  to  the  root  of  the  wing  (d),  the  angle 
at  which  the  wing  strikes  the  air  is  given.  The  body  and  wings  when  taken 
together  form  a  kite.  The  wings  in  the  partridge  are  rounded  and  broad. 
Compare  with  heron,  fig.  CO. — Original. 

than  the  air.  It  must  tread  and  rise  upon  the  air  as  a  swim- 
mer upon  the  water,  or  as  a  kite  upon  the  wind.  It  must 
act  against  gravity,  and  elevate  and  carry  itself  forward  at 
the  expense  of  the  air,  and  by  virtue  of  the  force  which 


Fio.  60.—  The  Grey  Heron  (Ardea  cineim^  in  fall  flight.  In  the  heron  the 
wings  are  deeply  concave,  and  unusually  large  as  compared  with  the  size  of 
the  bird.  The  result  is  that  the  wings  are  moved  very  leisurely,  with  a  slow, 
heavy,  and  almost  solemn  beat.  The  heron  figured  weighed  under  3  Ibs. : 
and  the  expanse  of  wing  was  considerably  greater  than  that  of  a  wild  goose 
which  weighed  over  9  Ibs.  Flight  is  consequently  more  a  question  of  power 
and  weight  than  of  buoyancy  and  surface,  d,  e,  f  Anterior  thick  strong 
margin  of  right  wing,  c,  a,  b  Posterior  thin  flexible  margin,  composed  of 
primary  (l>),  secondary  (a),  and  tertiary  (c)  feathers.  Compare  with  part- 
ridge, flg.  59. — Original. 

resides  in  it.  If  it  were  rescued  from  the  law  of  gravity  on 
the  one  hand,  and  bereft  of  independent  movement  on  the 
other,  it  would  float  about  uncontrolled  and  uncontrollable, 
as  happens  in  the  ordinary  gas-balloon 


PROGRESSION  IN  OK  THROUGH  THE  AIR.      127 

That  no  fixed  relation  exists  between  the  area  of  the  wings 
and  the  size  and  weight  of  the  body,  is  evident  on  comparing 
the  dimensions  of  the  wings  and  bodies  of  the  several  orders 
of  insects,  bats,  and  birds.  If  such  comparison  be  made,  it 
will  be  found  that  the  pinions  in  some  instances  diminish 
while  the  bodies  increase,  and  the  converse.  No  practical 
good  can  therefore  accrue  to  aerostation  from  elaborate 
measurements  of  the  wings  and  trunks  of  any  flying  thing ; 
neither  can  any  rule  be  laid  down  as  to  the  extent  of  surface 
required  for  sustaining  a  given  weight  in  the  air.  The  wing 
area  is,  as  a  rule,  considerably  in  excess  of  what  is  actually 
required  for  the  purposes  of  flight.  This  is  proved  in  two 
ways.  First,  by  the  fact  that  bats  can  carry  their  young  with- 
out inconvenience,  and  birds  elevate  surprising  quantities  of 
fish,  game,  carrion,  etc.  I  had  in  my  possession  at  one  time 
a  tame  barn-door  owl  which  could  lift  a  piece  of  meat  a 
quarter  of  its  own  weight,  after  fasting  four-and-twenty 
hours  ;  and  an  eagle,  as  is  well  known,  can  carry  a  moderate- 
sized  lamb  with  facility. 

The  excess  of  wing  area  is  proved,  secondly,  by  the  fact  that 
a  large  proportion  of  the  wings  of  most  volant  animals  may 
be  removed  without  destroying  the  power  of  flight.  I  in- 
stituted a  series  of  experiments  on  the  wings  of  the  fly, 
dragon-fly,  butterfly,  sparrow,  etc.,  with  a  view  to  determining 
this  point  in  1867.  The  following  are  the  results  obtained : — 

Slue-bottle  Fly. — Experiment  1.  Detached  posterior  or  thin 
half  of  each  wing  in  its  long  axis.  Flight  perfect. 

Exp.  2.  Detached  posterior  two-thirds  of  either  wing  in  its 
long  axis.  Flight  still  perfect.  I  confess  I  was  not  prepared 
for  this  result. 

Exp.  3.  Detached  one-third  of  anterior  or  thick  margin  of 
either  pinion  obliquely.  Flight  imperfect. 

Exp.  4.  Detached  one-half  of  anterior  or  thick  margin  of 
either  pinion  obliquely.  The  power  of  flight  completely 
destroyed.  From  experiments  3  and  4  it  would  seem  that 
the  anterior  margin  of  the  wing,  which  contains  the  principal 
nervures,  and  which  is  the  most  rigid  portion  of  the  pinion, 
cannot  be  mutilated  with  impunity. 

Exp.  5.  Removed  one-third  from  the  extremity  of  either 


128  ANIMAL  LOCOMOTION. 

wing  transversely,  i.e.  in  the  direction  of  the  short  axis  of 
the  pinion.  Flight  perfect. 

Exp.  6.  Removed  one-half  from  either  wing  transversely,  as 
in  experiment  5.  Flight  very  slightly  (if  at  all)  impaired. 

Exp.  7.  Divided  either  pinion  in  the  direction  of  its  long 
axis  into  three  equal  parts,  the  anterior  nervures  being  con- 
tained in  the  anterior  portion.  Flight  perfect. 

Exp.  8.  Notched  two-thirds  of  either  pinion  obliquely  from 
behind.  Flight  perfect. 

Exp.  9.  Notched  anterior  third  of  either  pinion  transversely. 
The  power  of  flight  destroyed.  Here,  as  in  experiment  4, 
the  mutilation  of  the  anterior  margin  was  followed  by  loss  of 
function. 

Exp.  10.  Detached  posterior  two-thirds  of  right  wing  in 
its  long  axis,  the  left  wing  being  untouched.  Flight  perfect. 
I  expected  that  this  experiment  would  result  in  loss  of 
balancing-power ;  but  this  was  not  the  case. 

Exp.  11.  Detached  half  of  right  wing  transversely,  the  left 
one  being  normal.  The  insect  flew  irregularly,  and  came  to 
the  ground  about  a  yard  from  where  I  stood.  I  seized  it 
and  detached  the  corresponding  half  of  the  left  wing,  after 
which  it  flew  away,  as  in  experiment  G. 

Dragon-Fly. — Exp.  12.  In  the  dragon-fly  either  the  first  or 
second  pair  of  wings  may  be  removed  without  destroying  the 
power  of  flight.  The  insect  generally  flies  most  steadily 
when  the  posterior  pair  of  wings  are  detached,  as  it  can  bal- 
ance better ;  but  in  either  case  flight  is  perfect,  and  in  no 
degree  laboured. 

Exp.  13.  Removed  one-third  from  the  posterior  margin  of 
the  first  and  second  pairs  of  wings.  Flight  in  no  wise  impaired. 

If  more  than  a  third  of  each  wing  is  cut  away  from  the 
posterior  or  thin  maigin,  the  insect  can  still  fly,  but  with 
effort. 

Experiment  13  shows  that  the  posterior  or  thin  flexible 
margins  of  the  wings  may  be  dispensed  with  in  flight.  They 
are  more  especially  engaged  in  propelling.  Compare  with 
experiments  1  and  2. 

Exp.  14.  The  extremities  or  tips  of  the  first  and  second 
pair  of  wings  may  be  detached  to  the  extent  of  one-third, 


PROGRESSION  IN  OR  THROUGH  THE  AIR.    •  129 

without  diminishing  the  power  of  flight.  Compare  with 
experiments  5  and  6. 

If  the  mutilation  be  carried  further,  flight  is  laboured,  and 
in  some  cases  destroyed. 

Exp.  15.  When  the  front  edges  of  the  first  and  second  pairs 
of  wings  are  notched  or  when  they  are  removed,  flight  is  com- 
pletely destroyed.  Compare  with  experiments  3,  4,  and  9. 

This  shows  that  a  certain  degree  of  stiffness  is  required  for 
the  front  edges  of  the  wings,  the  front  edges  indirectly  sup- 
porting the  back  edges.  It  is,  moreover,  on  the  front  edges 
of  the  wings  that  the  pressure  falls  in  flight,  and  by  these 
edges  the  major  portions  of  the  wings  are  attached  to  the 
body.  The  principal  movements  of  the  wings  are  communi- 
cated to  these  edges.- 

Butterfly. — Exp.  1 6.  Removed  posterior  halves  of  the  first 
pair  of  wings  of  white  butterfly.  Flight  perfect. 

Exp.  17.  Removed  posterior  halves  of  first  and  second 
pairs  of  wings.  Flight  not  strong  but  still  perfect.  If  addi- 
tional portions  of  the  posterior  wings  were  removed,  the 
insect  could  still  fly,  but  with  great  effort,  and  came  to  the 
ground  at  no  great  distance. 

Exp.  18.  When  the  tips  (outer  sixth)  of  the  first  and 
second  pairs  of  wings  were  cut  away,  flight  was  in  no  wise 
impaired.  When  more  was  detached  the  insect  could  not  fly. 

Exp.  19.  Removed  the  posterior  wings  of  the  brown  but- 
terfly. Flight  unimpaired. 

Exp.  20.  Removed  in  addition  a  small  portion  (one-sixth) 
from  the  tips  of  the  anterior  wings.  Flight  still  perfect,  as 
the  insect  flew  upwards  of  ten  yards. 

Exp.  21.  Removed  in  addition  a  portion  (one-eighth)  of 
the  posterior  margins  of  anterior  wings.  The  insect  flew 
imperfectly,  and  came  to  the  ground  about  a  yard  from  the 
point  where  it  commenced  its  flight. 

House  Sparrow. — The  sparrow  is  a  heavy  small-winged 
bird,  requiring,  one  would  imagine,  all  its  wing  area.  This, 
however,  is  not  the  case,  as  the  annexed  experiments  show. 

Exp.  22.  Detached  the  half  of  the  secondary  feathers  of 
either  pinion  in  the  direction  of  the  long  axis  of  the  wing, 
the  primaries  being  left  intact.  Flight  as  perfect  as  before 
7 


130  ANIMAL  LOCOMOTION, 

the  mutilation  took  place.  In  this  experiment,  one  wing  was 
operated  upon  before  the  other,  in  order  to  test  the  balancing- 
power.  The  bird  flew  perfectly,  either  with  one  or  with 
both  wings  cut. 

Exp.  23.  Detached  the  half  of  the  secondary  feathers  and 
a  fourth  of  the  primary  ones  of  either  pinion  in  the  long  axis 
of  the  wing.  Flight  in  no  wise  impaired.  The  bird,  in  this 
instance,  flew  upwards  of  30  yards,  and,  having  risen  a  con- 
siderable height,  dropped  into  a  neighbouring  tree. 

Exp.  24.  Detached  nearly  the  half  of  the  primary  feathers 
in  the  long  axis  of  either  pinion,  the  secondaries  being  left 
intact.  When  one  wing  only  was  operated  upon,  flight  was 
perfect ;  when  both  were  tampered  with,  it  was  still  perfect, 
but  slightly  laboured. 

Exp.  25.  Detached  rather  more  than  a  third  of  both 
primary  and  secondary  feathers  of  either  pinion  in  the  long 
axis  of  the  wing.  In  this  case  the  bird  flew  with  evident 
exertion,  but  was  able,  notwithstanding,  to  attain  a  very  con- 
siderable altitude. 

From  experiments  1,  2,  7,  8,  10,  13,  16,  22,  23,  24,  and 
25,  it  would  appear  that  great  liberties  may  be  taken  with 
the  posterior  or  thin  margin  of  the  wing,  and  the  dimensions 
of  the  wing  in  this  direction  materially  reduced,  without 
destroying,  or  even  vitiating  in  a  marked  degree,  the  powers 
of  flight.  This  is  no  doubt  owing  to  the  fact  indicated  by 
Sir  George  Cayley,  and  fully  explained  by  Mr.  Wenham,  that 
in  all  wings,  particularly  long  narrow  ones,  the  elevating 
power  is  transferred  to  the  anterior  or  front  margin.  These 
experiments  prove  that  the  upward  bending  of  the  posterior 
margins  of  the  wings  during  the  down  stroke  is  not  necessary 
to  flight. 

Exp.  26.  Removed  alternate  primary  and  secondary  feathers 
from  either  wing,  beginning  with  the  first  primary.  The  bird 
flew  upwards  of  fifty  yards  with  very  slight  effort,  rose  above 
an  adjoining  fence,  and  wheeled  over  it  a  second  time  to  settle 
on  a  tree  in  the  vicinity.  When  one  wing  only  was  oper- 
ated upon,  it  flew  irregularly  and  in  a  lopsided  manner. 

Exp.  27.  Removed  alternate  primary  and  secondary  feathers 
from  either  wing,  beginning  with  the  second  primary.  Flight, 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  131 

from  all  I  could  determine,  perfect.     When  one  wing  only 
was  cut,  flight  was  irregular  or  lopsided,  as  in  experiment  26. 

From  experiments  26  and  27,  as  well  as  experiments  7 
and  8,  it  would  seem  that  the  wing  does  not  of  necessity 
require  to  present  an  unbroken  or  continuous  surface  to  the 
air,  such  as  is  witnessed  in  the  pinion  of  the  bat,  and  that  the 
feathers,  when  present,  may  be  separated  from  each  other 
without  destroying  the  utility  of  the  pinion.  In  the  raven 
and  many  other  birds  the  extremities  of  the  first  four  or 
five  primaries  divaricate  in  a  marked  manner.  A  similar 
condition  is  met  with  in  the  Alucita  hexadactyla,  where  the 
delicate  feathery-looking  processes  composing  the  wing  are 
widely  removed  from  each  other.  The  wing,  however,  ceteris 
paribus,  is  strongest  when  the  feathers  are  not  separated  from 
each  other,  and  when  they  overlap,  as  then  they  are  arranged 
so  as  mutually  to  support  each  other. 

Exp.  28.  Removed  half  of  the  primary  feathers  from  either 
wing  transversely,  i.e.  in  the  direction  of  the  short  axis  of  the 
wing.  Flight  very  slightly,  if  at  all,  impaired  when  only  one 
wing  was  operated  upon.  When  both  were  cut,  the  bird  flew 
heavily,  and  came  to  the  ground  at  no  very  great  distance. 
This  mutilation  was  not  followed  by  the  same  result  in  ex- 
periments 6  and  11.  On  the  whole,  I  am  inclined  to  believe 
that  the  area  of  the  wing  can  be  curtailed  with  least  injury 
in  the  direction  of  its  long  axis,  by  removing  successive  por- 
tions from  its  posterior  margin. 

Exp.  29.  The  carpal  or  wrist-joint  of  either  pinion  ren- 
dered immobile  by  lashing  the  wings  to  slender  reeds,  the 
elbow-joints  being  left  free.  The  bird,  on  leaving  the  hand, 
fluttered  its  wings  vigorously,  but  after  a  brief  flight  came 
heavily  to  the  ground,  thus  showing  that  a  certain  degree  of 
twisting  and  folding,  or  flexing  of  the  wings,  is  necessary  to 
the  flight  of  the  bird,  and  that,  however  the  superficies  and 
shape  of  the  pinions  may  be  altered,  the  movements  thereof 
must  not  be  interfered  with.  1  tied  up  the  wings  of  a  pigeon 
in  the  same  manner,  with  a  precisely  similar  result. 

The  birds  operated  upon  were,  I  may  observe,  caught  in  a 
net,  and  the  experiments  made  within  a  few  minutes  from 
the  time  of  capture. 


132  ANIMAL  LOCOMOTION. 

Some  of  my  readers  will  probably  infer  from  the  foregoing, 
that  the  figure-of-8  curves  formed  along  the  anterior  and  pos- 
terior margins  of  the  pinions  are  not  necessary  to  flight,  since 
the  tips  and  posterior  margins  of  the  wings  may  be  removed 
without  destroying  it.  To  such  I  reply,  that  the  wings  are 
flexible,  elastic,  and  composed  of  a  congeries  of  curved  sur- 
faces, and  that  so  long  as  a  portion  of  them  remains,  they 
form,  or  tend  to  form,  figure-of-8  curves  in  every  direction. 

Captain  F.  W.  Hutton,  in  a  recent  paper  "  On  the  Flight 
of  Birds"  (Ibis,  April  1872),  refers  to  some  of  the  experi- 
ments detailed  above,  and  endeavours  to  frame  a  theory  of 
flight,  which  differs  in  some  respects  from  my  own.  His 
remarks  are  singularly  inappropriate,  and  illustrate  in  a  forci- 
ble manner  the  old  adage,  "  A  little  knowledge  is  a  danger- 
ous thing."  If  Captain  Hutton  had  taken  the  trouble  to  look 
into  my  memoir  "  On  the  Physiology  of  Wings,"  communi- 
cated to  the  Royal  Society  of  Edinburgh,  on  the  2d  of  August 
1870,1  fifteen  months  before  his  own  paper  was  written,  there 
is  reason  to  believe  he  would  have  arrived  at  very  different 
conclusions.  Assuredly  he  would  not  have  ventured  to  make 
the  rash  statements  he  has  made,  the  more  especially  as  he 
attempts  to  controvert  my  views,  which  are  based  upon  ana- 
tomical research  and  experiment,  without  making  any  dis- 
sections or  experiments  of  his  own. 

The  Wing  area  decreases  as  the  Size  and  Weight  of  the  Volant 
Animal  increases. — While,  as  explained  in  the  last  section,  no 
definite  relation  exists  between  the  weight  of  a  flying  animal 
and  the  size  of  its  flying  surfaces,  there  being,  as  stated,  heavy 
bodied  and  small- winged  insects,  bats,  and  birds,  and  the  con- 
verse ;  and  while,  as  I  have  shown  by  experiment,  flight  is 
possible  within  a  wide  range,  the  wings  being,  as  a  rule,  in 
excess  of  what  are  required  for  the  purposes  of  flight ;  still 
it  appears,  from  the  researches  of  M.  de  Lucy,  that  there  is  a 
general  law,  to  the  effect  that  the  larger  the  volant  animal 
the  smaller  by  comparison  are  its  flying  surfaces.  The  exist- 
ence of  such  a  law  is  very  encouraging  as  far  as  artificial 

1  •  On  the  Physiology  of  Wings,  being  an  Analysis  of  the  Movements  by 
Which  Flight  is  produced  in  the  Insect,  Bat,  and  Bird." — Trans.  Roy.  Soc.  of 
Edinburgh,  vol.  xxvi. 


PEOGEESSION  IN  Oil  THROUGH  THE  AIR. 


133 


flight  is  concerned,  for  it  shows  that  the  flying  surfaces  of  a 
large,  heavy,  powerful  flying  machine  will  be  comparatively 
small,  and  consequently  comparatively  compact  and  strong. 
This  is  a  point  of  very  considerable  importance,  as  the  object 
desiderated  in  a  flying  machine  is  elevating  capacity. 

M.  de  Lucy  has  tabulated  his  results,  which  I  subjoin  i1 — 


INSECTS. 

BIRDS. 

NAMES. 

Eeferrod  to  the 

—  211>8.  8oz.  3dwt.  2gr. 
Avoird. 
=  2  Ibs.  3  oz.  4-428  dr. 

NAiirJJ. 

Eeferred 
to  the 
kilogramme. 

Gnat,       

sq. 
yds.   ft     in. 
11     8     92 
7    2    56 
5  13    87 
5    2    89 
3    5     11 
1     2     74J 
1    3    54J 
1     2    20 
1     2    50 
1     1     39J 
0    8     33 
0    6  122J 

Swallow, 
Sparrow, 
Turtle-dove, 
Pigeon, 
Stork,    . 
Vulture, 
Crane  of  Australia, 

sq. 
yds.  ft.  In. 
1     1   104J 
0     5  142A 
0     4  100J 
0     2  113 
0    2    20 
0     1  116 
0    0  139 

Dragon-fly  (small), 
Coccinella  (Lady-bird), 
Dragon-fly  ((•.oniiuon),     . 
Tipula,  or  Daddy-long-legs,  . 
Bee,        

Meat-fly,         .... 

Drone  (blue), 
Cockchafer,    .... 
Lucanus  )  Stag  beetle  (female), 
cervus  \  Stag-beetle  (male), 
Rhinoceros-beetle,         . 

"  It  is  easy,  by  aid  of  this  table,  to  follow  the  order, 
always  decreasing,  of  the  surfaces,  in  proportion  as  the 
winged  animal  increases  in  size  and  weight.  Thus,  in  com- 
paring the  insects  with  oue  another,  we  find  that  the  gnat, 
which  weighs  460  times  less  than  the  stag-beetle,  has  four- 
teen times  more  of  surface.  The  lady-bird  weighs  150  times 
less  than  the  stag-beetle,  and  possesses  five  times  more  of 
surface.  It  is  the  same  with  the  birds.  The  sparrow 
weighs  about  ten  times  less  than  the  pigeon,  and  has  twice  as 
much  surface.  The  pigeon  weighs  about  eight  times  less 
than  the  stork,  and  has  twice  as  much  surface.  The  sparrow 
weighs  339  times  less  than  the  Australian  crane,  and  possesses 
seven  times  more  surface.  If  now  we  compare  the  in- 
sects and  the  birds,  the  gradation  will  become  even  much 
more  striking.  The  gnat,  for  example,  weighs  97,000  times 

1  "  On  the  Flight  of  Birds,  of  Bats,  and  of  Insects,  in  reference  to  the  sub- 
ject of  Aerial  Locomotion,"  by  M.  de  Lucy,  Paris. 


134  ANIMAL  LOCOMOTION. 

less  than  the  pigeon,  and  has  forty  times  more  surface ;  it 
weighs  3,000,000  times  less  than  the  crane  of  Australia, 
and  possesses  149  times  more  of  surface  than  this  latter,  the 
weight  of  which  is  about  9  kilogrammes  500  grammes  (25 
Ibs.  5  oz.  9  dwt.  troy,  20  Ibs.  15  oz.  2£  dr.  avoirdupois). 

The  Australian  crane  is  the  heaviest  bird  that  I  have 
weighed.  It  is  that  which  has  the  smallest  amount  of  sur- 
face, for,  referred  to  the  kilogramme,  it  does  not  give  us  a 
surface  of  more  than  899  square  centimetres  (139  square 
inches),  that  is  to  say  about  an  eleventh  part  of  a  square  metre. 
But  every  one  knoAvs  that  these  grallatorial  animals  are  excel- 
lent birds  of  flight.  Of  all  travelling  birds  they  undertake  the 
longest  and  most  remote  journeys.  They  are,  in  addition, 
the  eagle  excepted,  the  birds  which  elevate  themselves  the 
highest,  and  the  flight  of  which  is  the  longest  maintained."1 

Strictly  in  accordance  with  the  foregoing,  are  my  own 
measurements  of  the  gannet  and  heron.  The  following  de- 
tails of  weight,  measurement,  etc.,  of  the  gannet  were  supplied 
by  an  adult  specimen  which  I  dissected  during  the  winter  of 
1869.  Entire  weight,  7  Ibs.  (minus  3  ounces);  length  of 
body  from  tip  of  bill  to  tip  of  tail,  three  feet  four  inches ; 
head  and  neck,  one  foot  three  inches ;  tail,  twelve  inches ; 
trunk,  thirteen  inches ;  girth  of  trunk,  eighteen  inches ;  ex- 
panse of  wing  from  tip  to  tip  across  body,  six  feet ;  widest 
portion  of  wing  across  primary  feathers,  six  inches;  across 
secondaries,  seven  inches ;  across  tertiaries,  eight  inches.  Each 
wing,  when  carefully  measured  and  squared,  gave  an  area  of 
1 9 1  square  inches.  The  wings  of  the  gannet,  therefore,  fur- 
nish a  supporting  area  of  three  feet  three  inches  square.  As 
the  bird  weighs  close  upon  7  Ibs.,  this  gives  something  like 
thirteen  square  inches  of  wing  for  every  36  J  ounces  of  body, 
i,e.  one  foot  one  square  inch  of  wing  for  every  2  Ibs.  4£  oz. 
of  body. 

The  heron,  a  specimen  of  which  I  dissected  at  the  same 
time,  gave  a  very  different  result,  as  the  subjoined  particulars 
will  show.  Weight  of  body,  3  Ibs.  3  ounces ;  length  of  body 
from  tip  of  bill  to  tip  of  tail,  three  feet  four  inches ;  head  and 
neck,  two  feet ;  tail,  seven  inches ;  trunk,  nine  inches ;  girth 
i  M.  de  Lucy,  op.  cit. 


PROGRESSION  IN  OR  THROUGH  THE  AIR.      135 

of  body,  twelve  inches ;  expanse  of  wing  from  tip  to  tip  across 
the  body,  five  feet  nine  inches ;  widest  portion  of  wing  across 
primary  and  tertiary  feathers,  eleven  inches ;  across  secondary 
feathers,  twelve  inches. 

Each  wing,  when  carefully  measured  and  squared,  gave  an 
area  of  twenty-six  square  inches.  The  wings  of  the  heron, 
consequently,  furnish  a  supporting  area  of  four  feet  four  inches 
square.  As  the  bird  only  weighs  3  Ibs.  3  ounces,  this  gives 
something  like  twenty-six  square  inches  of  wing  for  every 
25  \  ounces  of  bird,  or  one  foot  5J  inches  square  for  every 
1  Ib.  1  ounce  of  body. 

In  the  gannet  there  is  only  one  foot  one  square  inch  of 
wing  for  every  2  Ibs.  4J  ounces  of  body.  The  gannet  has, 
consequently,  less  than  half  of  the  wing  area  of  the  heron. 
The  gannet's  wings  are,  however,  long  narrow  wings  (those 
of  the  heron  are  broad),  which  extend  transversely  across  the 
body;  and  these  are  found  to  be  the  most  powerful — the 
wings  of  the  albatross — which  measure  fourteen  feet  from  tip 
to  tip  (and  only  one  foot  across),  elevating  18  Ibs.  without 
difficulty.  If  the  wings  of  the  gannet,  which  have  a  super- 
ficial area  of  three  feet  three  inches  square,  are  capable  of 
elevating  7  Ibs.,  while  the  wings  of  the  heron,  whicla  have  a 
superficial  area  of  four  feet  four  inches,  can  only  elevate  3  Ibs., 
it  is  evident  (seeing  the  wings  of  both  are  twisted  levers,  and 
formed  upon  a  common  type)  that  the  gannet's  wings  must 
be  vibrated  with  greater  energy  than  the  heron's  wings ;  and 
this  is  actually  the  case.  The  heron's  wings,  as  I  have  ascer- 
tained from  observation,  make  60  down  and  60  up  strokes 
every  minute  ;  whereas  the  wings  of  the  gannet,  when  the 
bird  is  flying  in  a  straight  line  to  or  from  its  fishing-ground, 
make  close  upon  150  up  and  150  down  strokes  during  the 
same  period.  The  wings  of  the  divers,  and  other  short- winged, 
heavy-bodied  birds,  are  urged  at  a  much  higher  speed,  so  that 
comparatively  small  wings  can  be  made  to  elevate  a  compa- 
ratively heavy  body,  if  the  speed  only  be  increased  suffi- 
ciently.1 Flight,  therefore,  as  already  indicated,  is  a  ques- 

1  The  grebes  among  birds,  and  the  beetles  among  insects,  furnish  examples 
where  small  wings,  made  to  vibrate  at  high  speeds,  are  capable  of  elevating 
great  weights. 


136 


ANIMAL  LOCOMOTION. 


tion  of  power,  speed,  and  small  surfaces  versus  weight. 
Elaborate  measurements  of  wing,  area,  and  minute  calculations 
of  speed,  can  consequently  only  determine  the  minimum  of 
wing  for  elevating  the  maximum  of  weight — flight  being 
attainable  within  a  comparatively  wide  range. 

Wings,  tJieir  Form,  etc.;  all  Wings  Screics,  structurally  and 
functionally. — Wings  vary  considerably  as  to  their  general 
contour;  some  being  falcated  or  scythe-like,  some  oblong, 
some  rounded  or  circular,  some  lanceolate,  and  some  linear.1 

All  wings  are  constructed  upon  a  common  type.  They 
are  in  every  instance  carefully  graduated,  the  wing  tapering 

A 

S 


FIG.  61. — Right  wing  of  the  Kestrel,  drawn  from  the  specimen,  while  being 
held  against  the  light  Shows  how  the  primary  (b),  secondary  (a),  and  ter- 
tiary (c)  feathers  overlap  and  buttress  or  support  each  other  in  every  direc- 
tion. Each  set  of  feathers  has  its  coverts  and  subcoverts,  the  wing  being 
conical  from  within  outwards,  and  from  before  backwards,  d,  e,  /Anterior 
or  thick  margin  of  wing.  6,  a,  c  Posterior  or  thin  margin.  The  wing  of  the 
kestrel  is  intermediate  as  regards  form,  it  being  neither  rounded  as  iu  the 
partridge  (fig.  96,  p.  176),  nor  ribbon -shaped  as  in  the  albatross  (lig.  62),  nor 
pointed  as  in  the  swallow.  The  feathers  of  the  kestrel's  wing  are  unusually 
symmetrical  and  strong.  Compare  with  figs.  92,  94,  and  96,  pp.  174, 175,  and 
17(5. — Original. 

from  the  root  towards  the  tip,  and  from  the  anterior  margin 
in  the  direction  of  the  posterior  margin.  They  are  of  a 
generally  triangular  form,  and  twisted  upon  themselves  in  the 
direction  of  their  length,  to  form  a  helix  or  screw.  They 
are  convex  above  and  concave  below,  and  more  or  less  flexible 
and  elastic  throughout,  the  elasticity  being  greatest  at  the 
tip  and  along  the  posterior  margin.  They  are  also  moveable 
in  all  their  parts.  Figs.  61,  62,  63  (p.  138),  59  and  60 
(p.  126),  96  and  97  (p.  176),  represent  typical  bird  wings; 
figs.  17  (p.  36),  94  and  95  (p.  175),  typical  bat  wings;  and 
figs.  57  and  58  (p.  125),  89  and  90  (p.  171),  91  (p.  172),  92 
and  93  (p.  174),  typical  insect  wings. 

1  "The  wing  is  short,  broad,  convex,  and. rounded  in  grouse,  partridges, 
and  other  rasores  ;  long,  broad,  straight,  and  pointed  in  most  pigeons.  In  the 
peregrine  falcon  it  is  acuminate,  the  second  quill  being  longest,  and  the  first 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  137 

In  all  the  wings  which  I  have  examined,  whether  in  the 
insect,  bat,  or  bird,  the  wing  is  recovered,  flexed,  or  drawn 
towards  the  body  by  the  action  of  elastic  ligaments,  these 
structures,  by  their  mere  contraction,  causing  the  wing,  when 
fully  extended  and  presenting  its  maximum  of  surface,  to 
resume  its  position  of  rest  and  plane  of  least  resistance.  The 
principal  eifort  required  in  flight  is,  therefore,  made  during 
extension,  and  at  the  beginning  of  the  down  stroke.  The 
elastic  ligaments  are  variously  formed,  and  the  amount  of 
contraction  which  they  undergo  is  in  all  cases  accurately 
adapted  to  the  size  and  form  of  the  wing,  and  the  rapidity 
with  which  it  is  worked ;  the  contraction  being  greatest  in 
the  short-winged  and  heavy-bodied  insects  and  birds,  and 


FIG.  62.— Loft  wing  of  the  albatross,  d,  e,  /Anterior  or  thick  margin  of  pinion. 
6,  a,  c  Posterior  or  thin  margin,  composed  of  the  primary  (fc),  secondary  (a), 
and  tertiary  (c)  feathers.  In  this  wing  the  first  primary  is  the  longest,  the 
primary  coverts  and  subcoverts  being  unusually  long  and  strong.  The 
secondary  coverts  and  subcoverts  occupy  the  body  of  the  wing  (e,<7),  and  are 
so  numerous  as  effectually  to  prevent  any  escape  of  air  between  them  dur- 
ing the  return  or  up  stroke.  This  wing,  which  I  have  iu  my  possession, 
measures  over  six  feet  iu  length.  —  Original. 

least  in  the  light-bodied  and  ample-winged  ones,  particularly 
such  as  skim  or  glide.  The  mechanical  action  of  the  elastic 
ligaments,  I  need  scarcely  remark,  insures  an  additional 
period  of  repose  to  the  wing  at  each  stroke  ;  and  this  is  a 
point  of  some  importance,  as  showing  that  the  lengthened 
and  laborious  flights  of  insects  and  birds  are  not  without 
their  stated  intervals  of  rest. 

All  wings  are  furnished  at  their  roots  with  some  form  of 
universal  joint  which  enables  them  to  move  not  only  in  an 

little  shorter ;  and  in  the  swallows  this  is  still  more  the  case,  the  first  quill 
being  the  longest,  the  rest  rapidly  diminishing  in  length."— Macgillivray, 
Hist.  Brit.  Birds,  vol.  i.  p.  82.  "  The  hawks  have  been  classed  as  noble  or 
ignoble,  according  to  the  length  and  sharpness  of  their  wings  ;  and  the  fal- 
cons, or  long-winged  hawks,  are  distinguished  from  the  short-winged  ones  by 
the  second  feather  of  the  wing  being  either  the  longest  or  equal  in  length  to 
the  third,  and  by  the  nature  of  the  stoop  made  in  pursuit  of  their  prey." — 
Falconry  iu  the  British  Isles,  by  F.  H.  Salvin  and  W.  Brodrick.  Lond.  1855, 
p.  28. 


138  ANIMAL  LOCOMOTION. 

upward,  downward,  forward,  or  backward  direction,  but  also 
at  various  intermediate  degrees  of  obliquity.  All  wings 
obtain  their  leverage  by  presenting  oblique  surfaces  to  the 
air,  the  degree  of  obliquity  gradually  increasing  in  a  direction 
from  behind  forwards  and  downwards  during  extension  and 
the  down  stroke,  and  gradually  decreasing  in  an  opposite 
direction  during  flexion  and  the  up  stroke. 

In  the  insect  the  oblique  surfaces  are  due  to  the  conforma- 
tion of  the  shoulder-joint,  this  being  furnished  with  a  system 
of  check-ligaments,  and  with  horny  prominences  or  stops,  set, 


FIG.  63.—  The  Lapwing,  or  Green  Plover  (  VaneUus  crisiatus,  Meyer),  with  one 
wing  (c  ft,  d'  e'  f)  fully  extended,  and  forming  a  long  lever;  the  other  (d  ef, 
c  l>)  being  in  a  flexed  condition  and  forming  a  short  lever.  In  the  extended 
wing  the  anterior  or  thick  margin  (d' «'/')  >s  directed  upwards  and  forwards 
(vide  arrow),  the  posterior  or  thin  margin  (c,  b)  downwards  and  backward*. 
The  reverse  of  this  happens  during  flexion,  the  anterior  or  thick  margin 
(d,  e.f)  being  directed  downwards  and  forwards  (vide  arrow),  the  posterior 
or  thin  margin  (c  b)  bearing  the  rowing-feathers  upward*  and  backwards.  The 
wings  therefore  twist  in  opposite  directions  during  extension  and  flexion; 
and  this  is  a  point  of  the  utmost  importance  in  the  action  of  all  wings,  as  it 
enables  the  volant  animal  to  rotate  the  wings  on  and  off  the  air,  and  to  pre- 
sent at  one  time  (in  extension)  resisting,  kite-like  surfaces,  and  at  another  (in 
flexion)  knife-like  and  comparatively  non-resisting  surfaces.  It  rarely  happens 
in  flight  that  the  wing  (d  ef,  c  b)  is  so  fully  flexed  as  in  the  figure.  As  a  con- 
sequence, the  under  surface  of  the  wing  is,  as  a  rule,  inclined  upwards  and  for- 
wards, even  in  flexion,  so  that  it  acts  as  a  kite  in  extension  and  flexion,  and 
during  the  up  and  down  strokes. — Original. 

as  nearly  as  may  be,  at  right  angles  to  each  other.  The 
check -ligaments  and  horny  prominences  are  so  arranged  that 
when  the  wing  is  made  to  vibrate,  it  is  also  made  to  rotate 
in  the  direction  of  its  length,  in  the  manner  explained. 

In  the  bat  and  bird  the  oblique  surfaces  are  produced  by  the 
spiral  configuration  of  the  articular  surfaces  of  the  bones  of 


PKOGRESSION  IN  OR  THROUGH  THE  AIR. 


139 


the  wing,  and  by  the  rotation  of  the  bones  of  the  arm,  fore- 
arm, and  hand,  upon  their  long  axes.  The  reaction  of  the 
air  also  assists  in  the  production  of  the  oblique  surfaces. 

That  the  wing  twists  upon  itself  structurally,  not  only  in 
the  insect,  but  also  in  the  bat  and  bird,  any  one  may  readily 
satisfy  himself  by  a  careful  examination;  and  that  it  twists  upon 
itself  during  its  action  I  have  had  the  most  convincing  and  re- 
peated proofs  (figs.  64,  65,  and  66).  The  twisting  in  question 

Fio.  64. 


Fio.  65. 


Fio.  66. 


eft  wing  (a,  b)  of  wasp  in  the  act  of  twisting  upon  itself,  the  tip 
escribing  a  figure-of-8  track  (a,  c,  6).     From  nature. — Original. 


Fio.  64  shows  lef 

Fins.  65  and  66  show  right 'wing  of  blue-bottle  fly  rotating  on  its  anterior 
margin,  and  twisting  to  form  double  or  figure-of-8  curves  (a  &,  c  d).  From 
nature.  —Original. 


is  most  marked  in  the  posterior  or  thin  margin  of  the  wing,  the 
anterior  and  thicker  margin  performing  more  the  part  of  an  axis. 
As  a  result  of  this  arrangement,  the  anterior  or  thick  margin 
cuts  into  the  air  quietly,  and  as  it  were  by  stealth,  the  posterior 
one  producing  on  all  occasions  a  violent  commotion,  especially 
perceptible  if  a  flame  be  exposed  behind  the  vibrating  wing. 
Indeed,  it  is  a  matter  for  surprise  that  the  spiral  conformation 
of  the  pinion,  and  its  spiral  mode  of  action,  should  have 
eluded  observation  so  long ;  and  I  shall  be  pardoned  for 
dilating  upon  the  subject  when  I  state  my  conviction  that  it 


140  ANIMAL  LOCOMOTION. 

forms  the  fundamental  and  distinguishing  feature  in  flight, 
and  must  be  taken  into  account  by  all  who  seek  to  solve 
this  most  involved  and  interesting  problem  by  artificial  means. 
The  importance  of  the  twisted  configuration  or  screw-like 
form  of  the  wing  cannot  be  over-estimated.  That  this 
shape  is  intimately  associated  with  flight  is  apparent  from 
the  fact  that  the  rowing  feathers  of  the  wing  of  the  bird  are 
every  one  of  them  distinctly  spiral  in  their  nature ;  in  fact, 
one  entire  rowing  feather  is  equivalent — morphologically  and 
physiologically — to  one  entire  insect  wing.  In  the  wing  of 
the  martin,  where  the  bones  of  the  pinion  are  short  and  in 
some  respects  rudimentary,  the  primary  and  secondary  feathers 
are  greatly  developed,  and  banked  up  in  such  a  manner  that 
the  wing  as  a  whole  presents  the  same  curves  as  those  dis- 
played by  the  insect's  wing,  or  by  the  wing  of  the  eagle  where 
the  bones,  muscles,  and  feathers  have  attained  a  maximum 
development.  The  conformation  of  the  wing  is  such  that  it 
presents  a  waved  appearance  in  every  direction — the  waves 
running  longitudinally,  transversely,  and  obliquely.  The 
greater  portion  of  the  pinion  may  consequently  be  removed 
without  materially  affecting  either  its  form  or  its  functions. 
This  is  proved  by  making  sections  in  various  directions,  and 
by  finding,  as  has  been  already  shown,  that  in  some  instances 
as  much  as  two-thirds  of  the  wing  may  be  lopped  off  without 
visibly  impairing  the  power  of  flight.  The  spiral  nature  of 
the  pinion  is  most  readily  recognised  when  the  wing  is  seen 
from  behind  and  from  beneath,  and  when  it  is  foreshortened. 
It  is  also  well  marked  in  some  of  the  long-winged  oceanic 
birds  when  viewed  from  before  (figs.  82  and  83,  p.  158),  and 
cannot  escape  detection  under  any  circumstances,  if  sought 
for, — the  wing  being  essentially  composed  of  a  congeries  of 
curves,  remarkable  alike  for  their  apparent  simplicity  and  the 
subtlety  of  their  detail. 

The  Wing  during  its  action  reverses  its  Planes,  and  describes  a 
Figure-of-8  track  in  space. — The  twisting  or  rotating  of  the 
wing  on  its  long  axis  is  particularly  observable  during  exten- 
sion and  flexion  in  the  bat  and  bird,  and  likewise  in  the 
insect,  especially  the  beetle,  cockroach,  and  such  as  fold 
their  wings  during  repose.  In  these  in  extreme  flexion 


PROGRESSION  IN  OR  THROUGH  THE  AIR. 


141 


the  anterior  or  thick  margin  of  the  wing  is  directed  down- 
wards, and  the  posterior  or  thin  one  upwards.  In  the  act  of 
extension,  the  margins,  in  virtue  of  the  wing  rotating  upon  its 
long  axis,  reverse  their  positions,  the  anterior  or  thick  margins 
describing  a  spiral  course  from  below  upwards,  the  posterior 
or  thin  margin  describing  a  similar  but  opposite  course  from 
above  downwards.  These  conditions,  I  need  scarcely  observe, 
are  reversed  during  flexion.  The  movements  of  the  margins 
during  flexion  and  extension  may  be  represented  with  a  con- 
siderable degree  of  accuracy  by  a  figure-of-8  laid  horizontally. 
In  the  bat  and  bird  the  wing,  when  it  ascends  and  de- 
scends, describes  a  nearly  vertical  figure-of-8.  In  the  insect, 
the  wing,  from  the  more  oblique  direction  of  the  stroke, 


Fio.  67. 


FIG.  68. 


FIG.  60. 


FIG.  70. 


Fios.  67,  63,  69,  and  70,  show  the  area  mapped  out  by  the  left  wing  of  the 
wasp  when  the  insect  is  fixed  and  the  wing  made  to  vibrate.  These  figures 
illustrate  the  various  angles  made  by  the  wing  as  it  hastens  to  and  fro,  how 
the  wing  reverses  and  reciprocates,  and  how  it  twists  upon  itself  and  de- 
scribes a  flgure-of-8  track  in  space.  Figs.  67  and  69  represent  the  forward  or 
down  stroke;  Figs.  63  and  70  the  backward  or  up  stroke.  The  terms  for- 
ward and  back  stroke  are  here  employed  with  reference  to  the  head  of  the 
insect.— Original. 

describes  a  nearly  horizontal  figure-of-8.  In  either  case  the 
wing  reciprocates,  and,  as  a  rule,  reverses  its  planes.  The 
down  and  up  strokes,  as  will  be  seen  from  this  account,  cross 
each  other,  as  shown  more  particularly  at  figs.  67,  68,  69, 
and  70. 

In  the  wasp  the  wing  commences  the  down   or  forward 
stroke  at  a  of  figs.  67  and  69,  and  makes  an  angle  of  some- 


142  ANIMAL  LOCOMOTION. 

tiling  like  45°  with  the  horizon  (x  of).  At  b  (figs.  67  and  69) 
the  angle  is  slightly  diminished,  partly  because  of  a  rotation 
of  the  wing  along  its  anterior  margin  (long  axis  of  wing), 
partly  from  increased  speed,  and  partly  from  the  posterior 
margin  of  the  wing  yielding  to  a  greater  or  less  extent. 

At  c  the  angle  is  still  more  diminished  from  the  same 
causes. 

At  d  the  wing  is  slowed  slightly,  preparatory  to  reversing, 
and  the  angle  made  with  the  horizon  (x)  increased. 

At  e  the  angle,  for  the  same  reason,  is  still  more  increased; 
while  at  /  the  wing  is  at  right  angles  to  the  horizon.  It  is, 
in  fact,  in  the  act  of  reversing. 

At  g  the  wing  is  reversed,  and  the  up  or  back  stroke 
commenced. 

The  angle  made  at  g  is,  consequently,  the  same  as  that 
made  at  a  (45°),  with  this  difference,  that  the  anterior  margin 
and  outer  portion  of  the  wing,  instead  of  being  directed  Jor- 
wards,  with  reference  to  the  head  of  the  insect,  are  now 
directed  backwards. 

During  the  up  or  backward  stroke  all  the  phenomena  are 
reversed,  as  shown  at  g  h  ij  k  I  of  figs.  68  and  70  (p.  141);  the 
only  difference  being  that  the  angles  made  by  the  wing  with 
the  horizon  are  somewhat  less  than  during  the  down  or  forward 
stroke — a  circumstance  which  facilitates  the  forward  travel 
of  the  body,  while  it  enables  the  wing  during  the  back  stroke 
still  to  afford  a  considerable  amount  of  support.  This 
arrangement"  permits  the  wing  to  travel  backwards  while  the 
body  is  travelling  forwards;  the  diminution  of  the  angles 
made  by  the  wing  in  the  back  stroke  giving  very  much  the 
same  result  as  if  the  wing  were  striking  in  the  direction  of 
the  travel  of  the  body.  The  slight  upward  inclination  of  the 
wing  during  the  back  stroke  permits  the  body  to  fall  down- 
wards and  forwards  to  a  slight  extent  at  this  peculiar  junc- 
ture, the  fall  of  the  body,  as  has  been  already  explained, 
contributing  to  the  elevation  of  the  wing. 

The  pinion  acts  as  a  helix  or  screw  in  a  more  or  less  hori- 
zontal direction  from  behind  forwards,  and  from  before  back- 
wards ;  but  it  likewise  acts  as  a  screw  in  a  nearly  vertical 
direction.  If  the  wing  of  the  larger  domestic  fly  be  viewed 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  143 

during  its  vibrations  from  above,  it  will  be  found  that  the 
blur  or  impression  produced  on  the  dye  by  its  action  is  more 
or  less  concave  (fig.  66,  p.  139).  This  is  due  to  the  fact 
that  the  wing  is  spiral  in  its  nature,  and  because  during  its 
action  it  twists  upon  itself  in  such  a  manner  as  to  describe  a 
double  curve, — the  one  curve  being  directed  upwards,  the 
other  downwards.  The  double  curve  referred  to  is  particularly 
evident  in  the  flight  of  birds  from  •  the  greater  size  of  their 
wings.  The  wing,  both  when  at  rest  and  in  motion,  may  not 
inaptly  be  compared  to  the  blade  of  an  ordinary  screw  pro- 
peller as  employed  in  navigation.  Thus  the  general  outline 
of  the  wing  corresponds  closely  with  the  outline  of  the  blade 
of  the  propeller,  and  the  track  described  by  the  wing  in 
space  is  twisted  upon  itself  propeller  fashion.  The  great 
velocity  with  which  the  wing  is  driven  converts  the  impres- 
sion or  blur  into  what  is  equivalent  to  a  solid  for  the  time 
being,  in  the  same  way  that  the  spokes  of  a  wheel  in  violent 
motion,  as  is  well  understood,  completely  occupy  the  space 
contained  within  the  rim  or  circumference  of  the  wheel  (figs. 
64,  65,  and  66,  p.  139). 

The  figure-of  8  action  of  the  wing  explains  how  an  insect, 
bat,  or  bird,  may  fix  itself  in  the  air,  the  backward  and  for- 
ward reciprocating  action  of  the  pinion  affording  support,  but 
no  propulsion.  In  these  instances,  the  backward  and  forward 
strokes  are  made  to  counterbalance  each  other. 

The  Wing,  when  advancing  with  the  Body,  describes  a  Looped 
and  Waved  Track. — Although  the  figure-of-8  represents  with 
considerable  fidelity  the  twisting  of  the  wing  upon  its  long  axis 
during  extension  and  flexion,  and  during  the  down  and  up 
strokes  when  the  volant  animal  is  playing  its  wings  before  an 
object,  or  still  better,  when  it  is  artificially  fixed,  it  is  other- 
wise when  it  is  free  and  progressing  rapidly.  In  this  case  the 
wing,  in  virtue  of  its  being  carried  forward  by  the  body  in 
motion,  describes  first  a  looped  and  then  a  waved  track.  This 
looped  and  waved  track  made  by  the  wing  of  the  insect  is  re- 
presented at  figs.  71  and  72,  and  that  made  by  the  wing  of 
the  bat  and  bird  at  fig.  73,  p.  144. 

The  loops  made  by  the  wing  of  the  insect,  owing  to  the 
more  oblique  stroke,  are  more  horizontal  than  those  made  by 


144 


ANIMAL  LOCOMOTION. 


the  wing  of  the  bat  and  bird.  The  principle  is,  however,  in 
both  cases  the  same,  tile  loops  ultimately  terminating  in  a 
waved  track.  The  impulse  is  communicated  to  the  insect 
wing  at  the  heavy  parts  of  the  loops  a  bcdefghijklmn 
of  fig.  7 1  ;  the  waved  tracks  being  indicated  at  p  q  r  s  t  of 
the  same  figure.  The  recoil  obtained  from  the  air  is  repre- 
sented at  corresponding  letters  of  fig.  72,  the  body  of  the 

FIG.  71. 


FIG.  73. 

insect  being  carried  along  the  curve  indicated  by  the  dotted 
line.  The  impulse  is  communicated  to  the  wing  of  the  bat 
and  bird  at  the  heavy  part  of  the  loops  abcdefghijklmno 
of  fig.  73,  the  waved  track  being  indicated  at  p  s  t  u  v  w  of 
this  figure.  When  the  horizontal  speed  attained  is  high,  the 
wing  is  successively  and  rapidly  brought  into  contact  with 
innumerable  columns  of  undisturbed  air.  It,  consequently,  is 
a  matter  of  indifference  whether  the  wing  is  carried  at  a  high 
speed  against  undisturbed  air,  or  whether  it  operates  upon  air 


PROGRESSION  IN  OR  THROUGH  THE  AIR.      145 

travelling  at  a  high  speed  (as,  e.g.  the  artificial  currents  pro- 
duced by  the  rapidly  reciprocating  action  of  the  wing).  The 
result  is  the  same  in  both  cases,  inasmuch  as  a  certain  quan- 
tity of  air  is  worked  up  under  the  wing,  and  the  necessary 
degree  .of  support  and  progression  extracted  from  it.  It  is, 
therefore,  quite  correct  to  state,  that  as  the  horizontal  speed 
of  the  body  increases,  the  reciprocating  action  of  the  wing  de- 
creases ;  and  vice  versA.  In  fact  the  reciprocating  and  non- 
reciprocating  action  of  the  wing  in  such  cases  is  purely  a 
matter  of  speed.  If  the  travel  of  the  wing  is  greater  than  the 
horizontal  travel  of  the  body,  then  the  figure- of- 8  and  the 
reciprocating  power  of  the  wing  will  be  more  or  less  perfectly 
developed,  according  to  circumstances.  If,  however,  the 
horizontal  travel  of  the  body  is  greater  than  that  of  the 
wing,  then'  it  follows  that  no  figure  of- 8  will  be  described  by 
the  wing ;  that  the  wing  will  not  reciprocate  to  any  marked 


FIG.  74.  FIG.  75. 

FIGS.  74  and  75  show  the  more  or  less  perpendicular  direction  of  the  stroke  of  the 
wing  in  the  flight  of  the  bird  (gull) — how  the  wing  is  gradually  extended  as  it 
is  elevated  (efg  of  fig.  74)— how  it  descends  as  a  long  lever  until  it  assumes 
the  position  indicated  by  h  of  fig.  75— how  it  is  flexed  towards  the  termination 
of  the  down  stroke,  as  shown  at  A.  ij  of  fig.  75,  to  convert  it  into  a  short  lever 
(a  b)  and  prepare  it  for  making  the  up  stroke.  The  difference  in  the  length 
of  the  wing  during  flexion  and  extension  is  indicated  by  the  short  and  long 
levers  a  6  and  c  d  of  fig.  75.  The  sudden  conversion  of  the  wing  from  a  long 
into  a  short  lever  at  the  end  of  the  down  stroke  is  of  great  importance,  as  it 
robs  the  wing  of  its  momentum,  and  prepares  it  for  reversing  its  movements. 
Compare  with  figs.  82  and  83,  p.  158.— Original. 

extent ;  and  that  the  organ  will  describe  a  waved  track,  the 
curves  of  which  will  become  less  and  less  abrupt,  i.e.  longer" 
and  longer  in  proportion  to  the  speed  attained.  The  more 


146  ANIMAL  LOCOMOTION. 

vertical  direction  of  the  loops  formed  by  the  wing  of  the  bat 
and  bird  will  readily  be  understood  by  referring  to  figs. 
74  and  75  (p.  145),  which  represent  the  wing  of  the  bird 
making  the  down  and  up  strokes,  and  in  the  act  of  being  ex- 
tended and  flexed.  (Compare  with  figs.  64,  65,  and  66,  p. 
139 ;  and  figs.  67,  68,  69,  and  70,  p.  141.) 

The  down  and  up  strokes  are  compound  movements, — the 
termination  of  the  down  stroke  embracing  the  beginning  of 
the  up  stroke ;  the  termination  of  the  up  stroke  including  the 
beginning  of  the  down  stroke.  This  is  necessary  in  order 
that  the  down  and  up  strokes  may  glide  into  each  other  in 
such  a  manner  as  to  prevent  jerking  and  unnecessary  retarda- 
tion. 

The  Margins  of  tlie  Wing  thrown  into  opposite  Curves  during 
Extension  and  Flexion. — The  anterior  or  thick  margin  of  the 
wing,  and  the  posterior  or  thin  one,  form  different  curves, 
similar  in  all  respects  to  those  made  by  the  body  of  the 
fish  in  swimming  (see  fig.  32,  p.  68).  These  curves  may, 
for  the  sake  of  clearness,  be  divided  into  axillary  and  distal 
curves,  the  former  occurring  towards  the  root  of  the  wing, 
the  latter  towards  its  extremity.  The  curves  (axillary  and 
distal)  found  on  the  anterior  margin  of  the  wing  are 
always  the  converse  of  those  met  with  on  the  posterior 
margin,  i.e.  if  the  convexity  of  the  anterior  axillary  curve 
be  directed  downwards,  that  of  the  posterior  axillary  curve 
is  directed  upwards,  and  so  of  the  anterior  and  posterior 
distal  curves.  The  two  curves  (axillary  and  distal),  occurring 
on  the  anterior  margin  of  the  wing,  are  likewise  antagonistic, 
the  convexity  of  the  axillary  curve  being  always  directed 
downwards,  when  the  convexity  of  the  distal  one  is  directed 
upwards,  and  vice  versa.  The  same  holds  true  of  the  axillary 
and  distal  curves  occurring  on  the  posterior  margin  of  the 
wing.  The  anterior  axillary  and  distal  curves  completely 
reverse  themselves  during  the  acts  of  extension  and  flexion, 
and  so  of  the  posterior  axillary  and  distal  curves  (figs.  76,  77, 
and  78).  This  antagonism  in  the  axillary  and  distal  curves 
found  on  the  anterior  and  posterior  margins  of  the  wing  is 
referable  in  the  bat  and  bird  to  changes  induced  in  the  bones 
of  the  wins  in  the  acts  of  flexion  and  extension.  In  the 


PROGRESSION  IN  OR  THROUGH  THE  AIR. 


147 


insect  it  is  due  to  a  twisting  which  occurs  at  the  root  of  the 
wing  and  to  the  reaction  of  the  air. 


FIG.  76. 


FIG.  77. 


FIG.  78. 


FIG.  76.— Curves  seen  on  the  anterior  (d  e  f)  and  posterior  (c  a  6)  margin  in 
the  wing  of  the  bird  in  flexion. —Original. 

Fiu.  77.— Curves  seen  on  the  anterior  margin  (d  ef]  of  the  wing  in  semi-exten- 
sion. In  this  case  the  curves  on  the  posterior  margin  (6  c)  are  obliter- 
ated. — Original. 

FIG.  78. — Curves  seen  on  the  anterior  (def)  and  posterior  (c  a  V)  margin  of 
the  wing  in  extension.  The  curves  of  this  fig.  are  the  converse  of  those  seen 
at  fig.  76.  Compare  these  figs,  with  fig.  79  and  fig.  32,  p.  68.—  Original. 

The  Tip  of  the  Bat  and  Bird's  Wing  describes  an  Ellipse. — 
The  movements  of  the  wrist  are  always  the  converse  of  those 
occurring  at  the  elbow- joint.  Thus  in  the  bird,  during  ex- 
tension, the  elbow  and  bones  of  the  forearm  are  elevated,  and 
describe  one  side  of  an  ellipse,  while  the  wrist  and  bones  of 
the  hand  are  depressed,  and  describe  the  side  of  another 
and  opposite  ellipse.  These  movements  are  reversed  during 
flexion,  the  elbow  being  depressed  and  carried  backwards, 
while  the  wrist  is  elevated  and  carried  forwards  (fig.  79). 

Extension  (elbow).  Flexion  (wrist). 


Flexion  (elbow). 


Extension  (wrist). 


Fio.  79. — (a  V)  Line  along  which  the  wing  travels  during  extension  and  flexion. 
The  body  of  the  fish  in  swimming  describes  similar  curves  to  those  described 
by  the  wing  in  flying. — (Vide  fig.  32,  p.  68.) 

Tlie  Wing  capable  of  Change  of  Form  in  all  its  Parts. — From 
this  description  it  follows  that  when  the  different  portions  of 
the  anterior  margin  are  elevated,  corresponding  portions  of 
the  posterior  margin  are  depressed  ;  the  different  parts  of  the 
wing  moving  in  opposite  directions,  and  playing,  as  it  were, 
at  cross  purposes  for  a  common  good ;  the  object  being  to 
rotate  or  screw  the  wing  down  upon  the  wind  at  a  gradually 
increasing  angle  during  extension,  and  to  rotate  it  in  an 


148  ANIMAL  LOCOMOTION. 

opposite  direction  and  withdraw  it  at  a  gradually  decreasing 
angle  during  flexion.  It  also  happens  that  the  axillary  and 
distal  curves  co-ordinate  each  other  and  bite  alternately,  the 
distal  curve  posteriorly  seizing  the  air  in  extreme  extension 
with  its  concave  surface  (while  the  axillary  curve  relieves 
itself  by  presenting  its  convex  surface) ;  the  axillary  curve,  on 
the  other  hand,  biting  during  flexion  with  its  concave  surface 
(while  the  distal  one  relieves  itself  by  presenting  its  convex 
one).  The  wing  may  therefore  be  regarded  as  exercising  a 
fourfold  function,  the  pinion  in  the  bat  and  bird  being  made 
to  move  from  within  outwards,  and  from  above  downwards 
in  the  down  stroke,  during  extension;  and  from  without 
inwards,  and  from  below  upwards,  in  the  up  stroke,  during 
flexion. 

The  Wing  during  its  Vibration  produces  a  Cross  Pulsation. — 
The  oscillation  of  the  wing  on  two  separate  axes — the  one 
running  parallel  with  the  body  of  the  bird,  the  other  at  right 
angles  to  it  (fig.  80,  a  b,  c  d) — is  well  worthy  of  atten- 
tion, as  showing  that  the  wing  attacks  the  air,  on  which  it 
operates  in  every  direction,  and  at  almost  the  same  moment, 
viz.  from  within  outwards,  and  from  above  downwards, 
during  the  down  stroke;  and  from  without  inwards,  and 
from  below  upwards,  during  the  up  stroke.  As  a  corollary 
to  the  foregoing,  the  wing  may  be  said  to  agitate  the  air 
in  two  principal  directions,  viz.  from  within  outwards  and 
downwards,  or  the  converse ;  and  from  behind  forwards,  or 
the  converse ;  the  agitation  in  question  producing  two  power- 
ful pulsations,  a  vertical  and  a  horizontal.  The  wing  when 
it  ascends  and  descends  produces  artificial  currents  which 
increase  its  elevating  and  propelling  power.  The  power  of 
the  wing  is  further  augmented  by  similar  currents  developed 
during  its  extension  and  flexion.  The  movement  of  one  part 
of  the  wing  contributes  to  the  movement  of  every  other  part 
in  continuous  and  uninterrupted  succession.  As  the  curves 
of  the  wing  glide  into  each  other  when  the  wing  is  in  motion, 
so  the  one  pulsation  merges  into  the  other  by  a  series  of 
intermediate  and  lesser  pulsations. 

The  vertical  and  horizontal  pulsations  occasioned  by  the 
wing  in  action  may  be  fitly  represented  by  wave-tracks  running 


PROGRESSION  IN  OR  THROUGH  THE  AIR. 


149 


at  right  angles  to  each  other,  the  vertical  wave-track  being 
the  more  distinct. 

Compound  Rotation  of  the  Wing. — To  work  the  tip  and 
posterior  margin  of  the  wing  independently  and  yet  simul- 
taneously, two  axes  are  necessary,  one  axis  (the  short  axis) 
corresponding  to  the  root  of  the  wing  and  running  across 
it ;  the  second  (the  long  axis)  corresponding  to  the  anterior 
margin  of  the  wing,  and  running  in  the  direction  of  its  length. 
The  long  and  short  axes  render  the  movements  of  the  wing 
eccentric  in  character.  In  the  wing  of  the  bird  the  movements 
of  the  primary  or  rowing  feathers  are  also  eccentric,  the  shaft 
of  each  feather  being  placed  nearer  the  anterior  than  the  pos- 
terior margin ;  an  arrangement  which  enables  the  feathers  to 
open  up  and  separate  during  flexion  and  the  up  stroke,  and 
approximate  and  close  during  extension  and  the  down  one. 

These  points  are  illustrated  at  fig.  80,  where  a  b  represents 


the  short  axis  (root  of  wing)  with  a  radius  e  f;  c  d  represent- 
ing the  long  axis  (anterior  margin  of  wing)  with  a  radius  g  p. 
Fig.  80  also  shows  that,  in  the  wing  of  the  bird,  the  indi- 
vidual, primary,  secondary,  and  tertiary  feathers  have  each 
what  is  equivalent  to  a  long  and  a  short  axis.  Thus  the 
primary,  secondary,  and  tertiary  feathers  marked  h,  i,  j,  k,  I  are 
capable  of  rotating  on  their  long  axes  (r  s),  and  upon  their 
short  axes  (rn  ri).  The  feathers  rotate  upon  their  long  axes 
in  a  direction  from  below  upwards  during  the  down  stroke, 
to  make  the  wing  impervious  to  air ;  and  from  above  down- 


150  ANIMAL  LOCOMOTION. 

wards  during  the  up  stroke,  to  enable  the  air  to  pass  through 
it.  The  primary,  secondary,  and  tertiary  feathers  have  thus 
a  distinctly  valvular  action.1  The  feathers  rotate  upon  their 
short  axes  (m  n)  during  the  descent  and  ascent  of  the  wing, 
the  tip  of  the  feathers  rising  slightly  during  the  descent  of 
the  pinion,  and  falling  during  its  ascent.  The  same  move- 
ment virtually  takes  place  in  the  posterior  margin  of  the 
wing  of  the  insect  and  bat. 

The  Wing  vibrates  unequally  with  reference  to  a  given  Line. — 
The  wing,  during  its  vibration,  descends  further  below  the 
body  than  it  rises  above  it.  This  is  necessary  for  elevating 
purposes.  In  like  manner  the  posterior  margin  of  the  wing 
(whatever  the  position  of  the  organ)  descends  further  below 
the  anterior  margin  than  it  ascends  above  it.  This  is  re- 
quisite for  elevating  and  propelling  purposes;  the  under  surface 
of  the  wing  being  always  presented  at  a  certain  upward  angle 
to  the  horizon,  and  acting  as  a  true  kite  (figs.  82  and  83,  p. 
158.  Compare  with  fig.  116,  p.  231).  If  the  wing  oscil- 
lated equally  above  and  beneath  the  body,  and  if  the  pos- 
terior margin  of  the  wing  vibrated  equally  above  and  below 
the  line  formed  by  the  anterior  margin,  much  of  its  elevating 
and  propelling  power  would  be  sacrificed.  The  tail  of  the 
fish  oscillates  on  either  side  of  a  given  line,  but  it  is  other- 
wise with  the  wing  of  a  flying  animal.  The  fish  is  of  nearly 
the  same  specific  gravity  as  the  water,  so  that  the  tail  may 
be  said  only  to  propel.  The  flying  animal,  on  the  other 
hand,  is  very  much  heavier  than  the  air,  so  that  the  wing  re- 
quires both  to  propel  and  elevate.  The  wing,  to  be  effective  as 
an  elevating  organ,  must  consequently  be  vibrated  rather  below 
than  above  the  centre  of  gravity ;  at  all  events,  the  intensity 
of  the  vibration  should  occur  rather  below  that  point.  In 
making  this  statement,  it  is  necessary  to  bear  in  mind  that 
the  centre  of  gravity  is  ever  varying,  the  body  rising  and  falling 
in  a  series  of  curves  as  the  wings  ascend  and  descend. 

To  elevate  and  propel,  the  posterior  margin  of  the  wing  must 
rotate  round  the  anterior  one ;  the  posterior  margin  being,  as 
a  rule,  always  on  a  lower  level  than  the  anterior  one.  1'y 
the  oblique  and  more  vigorous  play  of  the  wings  under  rather 
than  above  the  body,  each  wing  expends  its  entire  energy  in 
1  The  degree  of  valvular  action  varies  according  to  circumstances. 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  151 

pushing  the  body  upwards  and  forwards.  It  is  necessary  that 
the  wings  descend  further  than  they  ascend ;  that  the  wings 
be  convex  on  their  upper  surfaces,  and  concave  on  their  under 
ones :  and  that  the  concave  or  biting  surfaces  be  brought 
more  violently  in  contact  with  the  air  during  the  down  stroke 
than  the  convex  ones  during  the  up  stroke.  The  greater 
range  of  the  wing  below  than  above  the  body,  and  of  the 
posterior  margin  below  than  above  a  given  line,  may  be 
readily  made  out  by  watching  the  flight  of  the  larger  birds. 
It  is  well  seen  in  the  upward  flight  of  the  lark.  In  the 
hovering  of  the  kestrel  over  its  quarry,  and  the  hovering  of 
the  gull  over  garbage  which  it  is  about  to  pick  up,  the  wings 
play  above  and  on  a  level  with  the  body  rather  than  below 
it ;  but  these  are  exceptional  movements  for  special  purposes, 
and  as  they  are  only  continued  for  a  few  seconds  at  a  time, 
do  not  affect  the  accuracy  of  the  general  statement. 

Points  wherein  the  Screws  formed  by  the  Wings  differ  from  those 
employed  in  navigation. — 1.  In  the  blade  of  the  ordinary  screw 
the  integral  parts  are  rigid  and  unyielding,  whereas,  in  the 
blade  of  the  screw  formed  by  the  wing,  they  are  mobile  and 
plastic  (figs.  93,  95,  97,  pp.  174, 175,  176).  This  is  a  curious 
and  interesting  point,  the  more  especially  as  it  does  not  seem 
to  be  either  appreciated  or  understood.  The  mobility  and 
plasticity  of  the  wing  is  necessary,  because  of  the  tenuity  of 
the  air,  and  because  the  pinion  is  an  elevating  and  sustaining 
organ,  as  well  as  a  propeQmg  one. 

2.  The  vanes  of  the  ordinary  two-bladed  screw  are  short, 
and  have  a  comparatively  limited  range,  the  range  corre- 
sponding to  their  area  of  revolution.  The  wings,  on  the 
other  hand,  are  long,  and  have  a  comparatively  wide  range; 
and  during  their  elevation  and  depression  rush  through 
an  extensive  space,  the  slightest  movement  at  the  root  or 
short  axis  of  the  wing  being  followed  by  a  gigantic  up 
or  down  stroke  at  the  other  (fig.  56,  p.  120;  figs.  64,  65, 
and  66,  p.  139  ;  figs.  82  and  83,  p.  158).  Asa  consequence, 
the  wings  as  a  rule  act  upon  successive  and  undisturbed  strata 
of  air.  The  advantage  gained  by  this  arrangement  in  a  thin 
medium  like  the  air,  where  the  quantity  of  air  to  be  com- 
pressed is  necessarily  great,  is  simply  incalculable. 


152  ANIMAL  LOCOMOTION. 

3.  In  the  ordinary  screw  the  blades  follow  each  other  in 
rapid  succession,  so  that  they  travel  over  nearly  the  same 
space,  and  operate  upon  nearly  the  same  particles  (whether 
water  or  air),  in  nearly  the  same  interval  of  time.  The 
limited  range  at  their  disposal  is  consequently  not  utilized,  the 
action  of  the  two  blades  being  confined,  as  it  were,  to  the 
same  plane,  and  the  blades  being  made  to  precede  or  follow 
each  other  in  such  a  manner  as  necessitates  the  work  being 
virtually  performed  only  by  one  of  them.  This  is  particularly 
the  case  when  the  motion  of  the  screw  is  rapid  and  the  mass 
propelled  is  in  the  act  of  being  set  in  motion,  i.e.  before  it 
has  acquired  momentum.  In  this  instance  a  large  percentage 
of  the  moving  or  driving  power  is  inevitably  consumed  in 
slip,  from  the  fact  of  the  blades  of  the  screw  operating  on 
nearly  the  same  particles  of  matter.  The  wings,  on  the  other 
hand,  do  not  follow  each  other,  but  have  a  distinct  recipro- 
cating motion,  i.e.  they  dart  first  in  one  direction,  and  then 
in  another  and  opposite  direction,  in  such  a  manner  that  they 
make  during  the  one  stroke  the  current  on  which  they  rise 
and  progress  the  next.  The  blades  formed  by  the  wings 
and  the  blur  or  impression  produced  on  the  eye  by  the  blades 
when  made  to  vibrate  rapidly  are  widely  separated, — the  one 
blade  and  its  blur  being  situated  on  the  right  side  of  the  body 
and  corresponding  to  the  right  wing,  the  other  on  the  left 
and  corresponding  to  the  left  wing.  The  right  wing  traverses 
and  completely  occupies  the  right  half  of  a  circle,  and  com- 
presses all  the  air  contained  within  this  space;  the  left 
wing  occupying  and  working  up  all  the  air  in  the  left  and 
remaining  half.  The  range  or  sweep  of  the  two  wings,  when 
urged  to  their  extreme  limits,  corresponds  as  nearly  as  may 
be  to  one  entire  circle1  (fig.  56,  p.  120).  By  separating 
the  blades  of  the  screw,  and  causing  them  to  reciprocate, 
a  double  result  is  produced,  since  the  blades  always  act  upon 
independent  columns  of  air,  and  in  .no  instance  overlap  or 
double  upon  each  other.  The  advantages  possessed  by  this 

1  Of  this  circle,  the  thorax  may  be  regarded  as  forming  the  centre,  the 
abdomen,  which  is  always  heavier  than  the  head,  tilting  the  body  slightly  in 
an  upward  direction.  This  tilting  of  the  trunk  favours  flight  by  causing  the 
body  to  act  after  the  manner  of  a  kite. 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  153 

arrangement  are  particularly  evident  when  the  motion  is 
rapid.  If  the  screw  employed  in  navigation  be  driven  beyond 
a  certain  speed,  it  cuts  out  the  water  contained  within  its 
blades  ;  the  blades  and  the  water  revolving  as  a  solid  mass. 
Under  these  circumstances,  the  propelling  power  of  the  screw 
is  diminished  rather  than  increased.  It  is  quite  otherwise 
with  the  screws  formed  by  the  wings ;  these,  because  of  their 
reciprocating  movements,  becoming  more  and  more  effective 
in  proportion  as  the  speed  is  increased.  As  there  seems  to 
be  no  limit  to  the  velocity  with  which  the  wings  may  be 
driven,  and  as  increased  velocity  necessarily  results  in  in- 
creased elevating,  propelling,  and  sustaining  power,  we  have 
here  a  striking  example  of  the  manner  in  which  nature 
triumphs  over  art  even  in  her  most  ingenious,  skilful,  and 
successful  creations. 

4.  The  vanes  or  blades  of  the  screw,  as  commonly  con- 
structed, are  fixed  at  a  given  angle,  and  consequently  always 
strike  at  the  same  degree  of  obliquity.  The  speed,  moreover, 
with  which  the  blades  are  driven,  is,  as  nearly  as  may  be, 
uniform.  In  this  arrangement  power  is  lost,  the  two  vanes 
striking  after  each  other  in  the  same  manner,  in  the  same 
direction,  and  almost  at  precisely  the  same  moment, — no 
provision  being  made  for  increasing  the  angle,  and  the  pro- 
pelling power,  at  one  stage  of  the  stroke,  and  reducing  it  at 
another,  to  diminish  the  amount  of  slip  incidental  to  the 
arrangement.  The  wings,  on  the  other  hand,  are  driven  at  a 
varying  speed,  and  made  to  attack  the  air  at  a  great  variety 
of  angles ;  the  angles  which  the  pinions  make  with  the  hori- 
zon being  gradually  increased  by  the  wings  being  made  to 
rotate  on  their  long  axes  during  the  down  stroke,  to  increase  the 
elevating  and  propelling  power,  and  gradually  decreased  during 
the  up  stroke,  to  reduce  the  resistance  occasioned  by  the  wings 
during  their  ascent.  The  latter  movement  increases  the  sustain- 
ing area  by  placing  the  wings  in  a  more  horizontal  position.  It' 
follows  from  this  arrangement  that  every  particle  of  air  within 
the  wide  range  of  the  wings  is  separately  influenced  by  them, 
both  during  their  ascent  and  descent, — the  elevating,  propel- 
ling, and  sustaining  power  being  by  this  means  increased  to  a 
maximum,  while  the  slip  or  waftage  is  reduced  to  a  minimum. 
8 


154  ANIMAL  LOCOMOTION. 

These  results  are  further  secured  by  the  undulatory  or  waved 
track  described  by  the  wing  during  the  down  and  up 
strokes.  It  is  a  somewhat  remarkable  circumstance  that 
the  wing,  when  not  actually  engaged  as  a  propeller  and  eleva- 
tor, acts  as  a  sustainer  after  the  manner  of  a  parachute.  This 
it  can  readily  do,  alike  from  its  form  and  the  mode  of  its 
application,  the  double  curve  or  spiral  into  which  it  is  thrown 
in  action  enabling  it  to  lay  hold  of  the  air  with  avidity,  in 
whatever  direction  it  is  urged.  I  say  "  in  whatever  direction," 
because,  even  when  it  is  being  recovered  or  drawn  off  the 
wind  during  the  back  stroke,  it  is  climbing  a  gradient  which 
arches  above  the  body  to  be  elevated,  and  so  prevents  it  from 
falling.  It  is  difficult  to  conceive  a  more  admirable,  simple, 
or  effective  arrangement,  or  one  which  would  more  thoroughly 
economize  power.  Indeed,  a  study  of  the  spiral  configuration 
of  the  wing,  and  its  spiral,  flail-like,  lashing  movements,  in- 
volves some  of  the  most  profound  problems  in  mathematics, 
— the  curves  formed  by  the  pinion  as  a  pinion  anatomically, 
and  by  the  pinion  in  action,  or  physiologically,  being  exceed- 
ingly elegant  and  infinitely  varied ;  these  ninning  into  each 
other,  and  merging  and  blending,  to  consummate  the  triple 
function  of  elevating,  propelling,  and  sustaining. 

Other  differences  might  be  pointed  out ;  but  the  foregoing 
embrace  the  more  fundamental  and  striking.  Enough,  more- 
over, has  probably  been  said  to  show  that  it  is  to  wing- 
structures  and  wing-movements  the  aeronaut  must  direct  his 
attention,  if  he  would  learn  "  the  way  of  an  eagle  in  the  air," 
and  if  he  would  rise  upon  the  whirlwind  in  accordance  with 
natural  laws. 

The  Wing  at  all  times  thoroughly  under  control. — The  wing 
is  moveable  in  all  parts,  and  can  be  wielded  intelligently 
even  to  its  extremity ;  a  circumstance  which  enables  the 
insect,  bat,  and  bird  to  rise  upon  the  air  and  tread  it  as  a 
master — to  subjugate  it  in  fact.  The  wing,  no  doubt,  abstracts 
an  upward  and  onward  recoil  from  the  air,  but  in  doing  this 
it  exercises  a  selective  and  controlling  power ;  it  seizes  one 
current,  evades  another,  and  creates  a  third ;  it  feels  and 
paws  the  air  as  a  quadruped  would  feel  and  paw  a  treacherous 
yielding  surface.  It  is  not  difficult  to  comprehend  why  this 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  155 

should  be  so.  If  the  flying  creature  is  living,  endowed  with 
volition,  and  capable  of  directing  its  own  course,  it  is  surely 
more  reasonable  to  suppose  that  it  transmits  to  its  travelling 
surfaces  the  peculiar  movements  necessary  to  progression,  than 
that  those  movements  should  be  the  result  of  impact  from 
fortuitous  currents  which  it  has  no  means  of  regulating.  That 
the  bird,  e.g.  requires  to  control  the  wing,  and  that  the  wing 
requires  to  be  in  a  condition  to  obey  the  behests  of  the  will 
of  the  bird,  is  pretty  evident  from  the  fact  that  most  of  our 
domestic  fowls  can  fly  for  considerable  distances  when  they 
are  young  and  when  their  wings  are  flexible ;  whereas  when 
they  are  old  and  the  wings  stiff,  they  either  do  not  fly  at  all 
or  only  for  short  distances,  and  with  great  difficulty.  This 
is  particularly  the  case  with  tame  swans.  This  remark  also 
holds  true  of  the  steamer  or  race-horse  duck  (Anas  brachy- 
ptera),  the  younger  specimens  of  which  only  are  volant.  In 
older  birds  the  wings  become  too  rigid  and  the  bodies  too 
heavy  for  flight.  Who  that  has  watched  a  sea-mew  struggling 
bravely  with  the  storm,  could  doubt  for  an  instant  that  the 
wings  and  feathers  of  the  wings  are  under  control  ?  The  whole 
bird  is  an  embodiment  of  animation  and  power.  The  intelli- 
gent active  eye,  the  easy,  graceful,  oscillation  of  the  head  and 
neck,  the  folding  or  partial  folding  of  one  or  both  wings,  nay 
more,  the  slight  tremor  or  quiver  of  the  individual  feathers 
of  parts  of  the  wings  so  rapid,  that  only  an  experienced  eye 
can  detect  it,  all  confirm  the  belief  that  the  living  wing  has 
not  only  the  power  of  directing,  controlling,  and  utilizing 
natural  currents,  but  of  creating  and  utilizing  artificial  ones. 
But  for  this  power,  what  would  enable  the  bat  arid  bird  to 
rise  and  fly  in  a  calm,  or  steer  their  course  in  a  gale  ?  It  is 
erroneous  to  suppose  that  anything  is  left  to  chance  where 
living  organisms  are  concerned,  or  that  animals  endowed  with 
volition  and  travelling  surfaces  should  be  denied  the  privilege 
of  controlling  the  movements  of  those  surfaces  quite  independ- 
ently of  the  medium  on  which  they  are  destined  to  operate. 
I  will  never  forget  the  gratification  afforded  me  on  one  occa- 
sion at  Carlo w  (Ireland)  by  the  flight  of^a  pair  of  magnificent 
swans.  The  birds  flew  towards  and  past  me,  my  attention 
having  been  roused  by  a  peculiarly  loud  whistling  noise 


156  ANIMAL  LOCOMOTION. 

made  by  their  wings.  They  flew  about  fifteen  yards  from  the 
ground,  and  as  their  pinions  were  urged  not  much  faster  than 
those  of  the  heron,1  I  had  abundant  leisure  for  studying  their 
movements.  The  sight  was  very  imposing,  and  as  novel  as  it 
was  grand.  I  had  seen  nothing  before,  and  certainly  have 
seen  nothing  since  that  could  convey  a  more  elevated  concep- 
tion of  the  prowess  and  guiding  power  which  birds  may 
exert.  What  particularly  struck  me  was  the  perfect  command 
they  seemed  to  have  over  themselves  and  the  medium  they 
navigated.  They  had  their  wings  and  bodies  visibly  under 
control,  and  the  air  was  attacked  in  a  manner  and  with  an 
energy  which  left  little  doubt  in  my  mind  that  it  played  quite 
a  subordinate  part  in  the  great  problem  before  me.  The 
necks  of  the  birds  were  stretched  out,  and  their  bodies  to  a 
great  extent  rigid.  They  advanced  with  a  steady,  stately 
motion,  and  swept  past  with  a  vigour  and  force  which  greatly 
impressed,  and  to  a  certain  extent  overawed,  me.  Their 
flight  was  what  one  could  imagine  that  of  a  flying  machine 
constructed  in  accordance  with  natural  laws  would  be.2 

The  Natural  Wing,  when  elevated  and  depressed,  must  move 
forwards. — It  is  a  condition  of  natural  wings,  and  of  artificial 
wings  constructed  on  the  principle  of  living  wings,  that  when 

1 1  have  frequently  timed  the  beats  of  the  wings  of  the  Common  Heron 
(Ardea  cinerea)  in  a  heronry  at  Warren  Point.  In  March  1869  I  was  placed 
under  unusually  favourable  circumstances  for  obtaining  trustworthy  results. 
I  timed  one  bird  high  up  over  a  lake  in  the  vicinity  of  the  heronry  for  fifty 
seconds,  and  found  that  in  that  period  it  made  fifty  down  and  fifty  up  strokes  ; 
i.e.  one  down  and  one  up  stroke  per  second.  I  timed  another  one  in  the 
heronry  itself.  It  was  snowing  at  the  time  (March  1869),  but  the  birds,  not- 
withstanding the  inclemency  of  the  weather  and  the  early  time  of  the  year, 
were  actively  engaged  in  hatching,  and  required  to  be  driven  from  their 
nests  on  the  top  of  the  larch  trees  by  knocking  against  the  trunks  thereof  with 
large  sticks.  One  unusually  anxious  mother  refused  to  leave  the  immediate 
neighbourhood  of  the  tree  containing  her  tender  charge,  and  circled  round  and 
round  it  right  overhead.  I  timed  this  bird  for  ten  seconds,  and  found  that 
she  made  ten  down  and  ten  up  strokes  ;  i.e.  one  down  and  one  up  stroke 
per  second  precisely  as  before.  I  have  therefore  no  hesitation  in  affirming 
that  the  heron,  in  ordinary  flight,  makes  exactly  sixty  down  and  sixty  up 
strokes  per  minute.  The  heron,  however,  like  all  other  birds  when  pursued 
or  agitated,  has  the  power%  of  greatly  augmenting  the  number  of  beats  made 
by  its  wings. 

2  The  above  observation  was  made  at  Carlow  on  the  Barrow  in  October 
1867,  and  the  account  of  it  is  taken  from  my  note-book. 


PROGRESSION  IN  OR -THROUGH  THE  AIR.  157 

forcibly  elevated  or  depressed,  even  in  a  strictly  vertical 
direction,  they  inevitably  dart  forward.  This  is  well  shown 
in  fig.  81. 


FIG.  81. 

If,  for  example,  the  wing  is  suddenly  depressed  in  a  vertical 
direction,  as  represented  at  a  b,  it  at  once  darts  downwards 
and  forwards  in  a  curve  to  c,  thus  converting  the  vertical 
down  stroke  into  a  down  oblique  forward  stroke.  If,  again,  the 
wing  be  suddenly  elevated  in  a  strictly  vertical  direction,  as 
at  c  d,  the  wing  as  certainly  darts  upwards  and  forwards  in 
a  curve  to  e,  thus  converting  the  vertical  up  stroke  into  an 
upward  oblique  forward  stroke.  The  same  thing  happens  when 
the  wing  is  depressed  from  e  to  /,  and  elevated  from  g  to  h. 
In  both  cases  the  wing  describes  a  waved  track,  as  shown  at 
e  g,  g  i,  which  clearly  proves  that  the  wing  strikes  downwards 
and  forwards  during  the  down  stroke,  and  upwards  and  forwards 
during  the  up  stroke.  The  wing,  in  fact,  is  always  advancing ; 
its  under  surface  attacking  the  air  like  a  boy's  kite.  If,  on 
the  other  hand,  the  wing  be  forcibly  depressed,  as  indicated 
by  the  heavy  waved  line  a  c,  and  left  to  itself,  it  will  as  surely 
rise  again  and  describe  a  waved  track,  as  shown  at  c  e.  This 
it  does  by  rotating  on  its  long  axis,  and  in  virtue  of  its  flexi- 
bility and  elasticity,  aided  by  the  recoil  obtained  from  the 
air.  In  other  words,  it  is  not  necessary  to  elevate  the  wing 
forcibly  in  the  direction  c  d  to  obtain  the  upward  and  forward 
movement  c  e.  One  single  impulse  communicated  at  a  causes 
the  wing  to  travel  to  e,  and  a  second  impulse  communicated 
at  e  causes  it  to  travel  to  i.  It  follows  from  this  that  a  series 
of  vigorous  down  impulses  would,  if  a  certain  interval  were 
allowed  to  elapse,  between  them,  -beget  a  corresponding  series  of 
up  impulses,  in  accordance  with  the  law  of  action  and  re- 
action ;  the  wing  and  the  air  under  these  circumstances  being 
alternately  active  and  passive.  I  say  if  a  certain  interval 
were  allowed  to  elapse  between  every  two  down  strokes,  but 


158 


ANIMAL  LOCOMOTION. 


this  is  practically  impossible,  as  the  wing  is  driven  with  such 
velocity  that  there  is  positively  no  time  to  waste  in  waiting 
for  the  purely  mechanical  ascent  of  the  wing.  That  the 


FIG.  82. 


Fio.  83. 

Figs.  82  and  83  show  that  when  the  wings  are  elevated  (e,  f,  g  of  fig.  82)  the 
body  falls  (s  of  fig.  82)  ;  and  that  when  the  wings  are  depressed  (h,  i,  j  of 
flg.  83)  the  body  is  elevated  (r  of  fig.  83).  Fig.  82  shows  that  the  wings  are 
elevated  as  short  levers  (e)  until  towards  the  termination  of  the  up  stroke; 
•when  they  are  gradually  expanded  (J,  g)  to  prepare  them  for  making  the 
down  stroke.  Fig.  83  shows  that  the  wings  descend  as  long  levers  (h]  until 
towardsfce  termination  of  the  down  stroke,  when  they  are  gradually  folded 
or  flexed  (i,  j),  to  rob  them  of  their  momentum  and  prepare  them  for  making 
the  up  stroke.  Compare  with  figs.  74  and  75,  p.  145.  By  this  means  the  air 
beneath  the  wings  is  vigorously  seized  during  the  down  stroke,  while  that 
above  it  is  avoided  during  the  up  stroke.  The  concavo-convex  form  of  the 
wings  and  the  forward  travel  of  the  body  contribute  to  this  result.  The 
wings,  it  will  be  observed,  act  as  a  parachute  both  during  the  up  and  down 
strokes.  Compare  with  fig.  55,  p.  112.  Fig.  83  shows,  in  addition,  the  com- 
pound rotation  of  the  wing,  how  it  rotates  upon  a  as  a  centre,  with  a  radius 
m  b  n,  and  upon  a  c  b  as  a  centre,  with  a  radius  k  I.  Compare  with  fig.  80, 
p.  149.— Original 

ascent  of  the  pinion  is  not,  and  ought  not  to  be  entirely  due 
to  the  reaction  of  the  air,  is  proved  by  the  fact  that  in  flying 
creatures  (certainly  in  the  bat  and  bird)  there  are  distinct 


PROGRESSION  IN  OR  THROUGH  THE  AIB.      159 

elevator  muscles  and  elastic  ligaments  delegated  to  the  per- 
formance of  this  function.  The  reaction  of  the  air  is  there- 
fore only  one  of  the  forces  employed  in  elevating  the  wing ; 
the  others,  as  I  shall  show  presently,  are  vital  and  vito- 
mechanical  in  their  nature.  The  falling  downwards  and  for- 
wards of  the  body  when  the  wings  are  ascending  also  contri- 
bute to  this  result. 

The  Wing  ascends  when  the  Body  descends,  and  vice  versa. — 
As  the  body  of  the  insect,  bat,  and  bird  falls  forwards  in  a 
curve  when  the  wing  ascends,  and  is  elevated  in  a  curve  when 
the  wing  descends,  it  follows  that  the  trunk  of  the  animal  is 
urged  along  a  waved  line,  as  represented  at  1,  2,  3,  4,  5  of 
n'g.  81,  p.  157  ;  the  waved  line  a  c  e  gi  of  the  same  figure 
giving  the  track  made  by  the  wing.  I  have  distinctly  seen 
the  alternate  rise  and  fall  of  the  body  and  wing  when  watch- 
ing the  flight  of  the  gull  from  the  stern  of  a  steam-boat. 

The  direction  of  the  stroke  in  the  insect,  as  has  been  already 
explained,  is  much  more  horizontal  than  in  the  bat  or  bird 
(compare  figs.  82  and  83  with  figs.  64,  65,  and  66,  p.  1 39).  In 
either  case,  however,  the  down  stroke  must  be  delivered  in  a 
more  or  less  forward  direction.  This  is  necessary  for  support 
and  propulsion.  A  horizontal  to-and-fro  movement  will  elevate, 
and  an  up-and-down  vertical  movement  propel,  but  an  oblique 
forward  motion  is  requisite  for  progressive  flight. 

In  all  wings,  whatever  their  position  during  the  intervals 
of  rest,  and  whether  in  one  piece  or  in  many,  this  feature  is 
to  be  observed  in  flight.  The  wings  are  slewed  downwards 
and  forwards,  i.e.  they  are  carried  more  or  less  in  the  direc- 
tion of  the  head  during  their  descent,  and  reversed  or  carried 
in  an  opposite  direction  during  their  ascent.  In  stating  that 
the  wings  are  carried  away  from  the  head  during  the  back 
stroke,  I  wish  it  to  be  understood  that  they  do  not  therefore 
necessarily  travel  backwards  in  space  when  the  insect  is  flying 
forwards.  On  the  contrary,  the  wings,  as  a  rule,  move  for- 
ward in  curves,  both  during  the  down  and  up  strokes.  The 
fact  is,  that  the  wings  at  their  roots  are  hinged  and  geared  to 
the  trunk  so  loosely,  that  the  body  is  free  to  oscillate  in  a 
forward  or  backward  direction,  or  in  an  up,  down,  or  oblique 
direction.  As  a  consequence  of  this  freedom  of  movement. 


160 


ANIMAL  LOCOMOTION. 


and  as  a  consequence  likewise  of  the  speed  at  which  the  insect 
is  travelling,  the  wings  during  the  back  stroke  are  for  the 
most  part  actually  travelling  forwards.  This  is  accounted  for 
by  the  fact,  that  the  body  falls  downwards  and  forwards  in  a 
curve  during  the  up  or  return  stroke  of  the  wings,  and  be- 
cause the  horizontal  speed  attained  by  the  body  is  as  a  rule 
so  much  greater  than  that  attained  by  the  wings,  that  the 
latter  are  never  allowed  time  to  travel  backward,  the  lesser 
movement  being  as  it  were  swallowed  up  by  the  greater.  For 
a  similar  reason,  the  passenger  of  a  steam-ship  may  travel 
rapidly  in  the  direction  of  the  stern  of  the  vessel,  and  yet  be 
carried  forward  in  space, — the  ship  sailing  much  quicker  than 
he  can  walk.  While  the  wing  is  descending,  it  is  rotating 
upon  its  root  as  a  centre  (short  axis).  It  is  also,  and  this  is 
a  most  important  point,  rotating  upon  its  anterior  margin 
(long  axis),  in  such  a  manner  as  to  cause  the  several  parts 
of  the  wing  to  assume  various  angles  of  inclination  with  the 
horizon. 

Figs.  84  and  85  supply  the  necessary  illustration. 


FIG.  84. 


<*k- 


FIG.  85. 

In  flexion,  as  a  rule,  the  under  surface  of  the  wing  (fig.  84 
a)  is  arranged  in  the  same  plane  with  the  body,  both  being  in 
a  line  with  or  making  a  slight  angle  with  the  horizon  (x  x).1 

1  It  happens  occasionally  in  insects  that  the  posterior  margin  of  the  wing 
is  on  a  higher  level  than  the  anterior  one  towards  the  termination  of  the  up 
stroke.  In  such  cases  the  posterior  margin  is  suddenly  rotated  in  a  downward 


PROGRESSION  IN  OR  THROUGH  THE  AIR. 


161 


When  the  wing  is  made  to  descend,  it  gradually,  in  virtue  of 
its  simultaneously  rotating  upon  its  long  and  short  axes, 
makes  a  certain  angle  with  the  horizon  as  represented  at  b. 
The  angle  is  increased  at  the  termination  of  the  down  stroke 
as  shown  at  c,  so  that  the  wing,  particularly  its  posterior 
margin,  during  its  descent  (A\  is  screwed  or  crashed  down 
upon  the  air  with  its  concave  or  biting  surface  directed  for- 
wards and  towards  the  earth.  The  same  phenomena  are 
indicated  at  a  b  c  of  fig.  85,  but  in  this  figure  the  wing  is 
represented  as  travelling  more  decidedly  forwards  during  its 
descent,  and  this  is  characteristic  of  the  down  stroke  of  the 
insect's  wing — the  stroke  in  the  insect  being  delivered  in  a 
very  oblique  and  more  or  less  horizontal  direction  (figs.  64, 
65,  and  66,  p.  139 ;  fig.  71,  p.  144).  The  forward  travel  of 
the  wing  during  its  descent  has  the  effect  of  diminishing  the 
angles  made  by  the  under  surface  of  the  wing  with  the  hori- 
zon. Compare  bed  of  fig.  85  with  the  same  letters  of  fig.  84. 


At  fig.  88  (p.  166)  the  angles  for  a  similar  reason  are  still 
further  diminished.  This  figure  (88)  gives  a  very  accurate 
idea  of  the  kite-like  action  of  the  wing  both  during  its 
descent  and  ascent. 

The  downward  screwing  of  the  posterior  margin  of  the 

and  forward  direction  at  the  beginning  of  the  down  stroke — the  downward  and 
forward  rotation  securing  additional  elevating  power  for  the  wing.  The  pos- 
terior margin  of  the  wing  in  bats  and  birds,  unless  they  are  flying  downwards, 
never  rises  above  the  anterior  one,  either  during  the  up  or  down  stroke. 


162  ANIMAL  LOCOMOTION. 

wing  during  the  down  stroke  is  well  seen  in  the  dragon-fly, 
represented  at  fig.  86,  p.  161. 

Here  the  arrows  rs  indicate  the  range  of  the  wing.  At 
the  beginning  of  the  down  stroke  the  upper  or  dorsal  sur- 
face of  the  wing  (i  d  f)  is  inclined  slightly  upwards  and  for- 
wards. As  the  wing  descends  the  posterior  margin  (if) 
twists  and  rotates  round  the  anterior  margin  (i  d),  and  greatly 
increases  the  angle  of  inclination  as  seen  at  ij,  g  h.  This  rota- 
tion of  the  posterior  margin  (if)  round  the  anterior  margin 
(g  li)  has  the  effect  of  causing  the  different  portions  of  the  under 
surface  of  the  wing  to  assume  various  angles  of  inclination 
with  the  horizon,  the  wing  attacking  the  air  like  a  boy's  kite. 
The  angles  are  greatest  towards  the  root  of  the  wing  and  least 
towards  the  tip.  They  accommodate  themselves  to  the  speed 
at  which  the  different  parts  of  the  wing  travel — a  small 
angle  with  a  high  speed  giving  the  same  amount  of  buoying 
power  as  a  larger  angle  with  a  diminished  speed.  The  screw- 
ing of  the  under  surface  of  the  wing  (particularly  the  posterior 
margin)  in  a  downward  direction  during  the  down  stroke  is 
necessary  to  insure  the  necessary  upward  recoil;  the  wing 
being  made  to  swing  downwards  and  forwards  pendulum 
fashion,  for  the  purpose  of  elevating  the  body,  which  it  does  by 
acting  upon  the  air  as  a  long  lever,  and  after  the  manner  of  a 
kite.  During  the  down  stroke  the  wing  is  active,  the  air  passive. 
In  other  words,  the  wing  is  depressed  by  a  purely  vital  act. 

The  down  stroke  is  readily  explained,  and  its  results 
upon  the  body  obvious.  The  real  difficulty  begins  with 
the  up  or  return  stroke.  If  the  wing  was  simply  to  travel  in 
an  upward  and  backward  direction  from  c  to  a  of  fig.  84, 
p.  160,  it  is  evident  that  it  would  experience  much  resistance 
from  the  superimposed  air,  and  thus  the  advantages  secured 
by  the  descent  of  the  wing  would  be  lost.  What  really 
happens  is  this.  The  wing  does  not  travel  upwards  and 
backwards  in  the  direction  cba  of  fig.  84  (the  body,  be  it 
remembered,  is  advancing)  but  upwards  and  forwards  in  the 
direction  c  d  e  f  g.  This  is  brought  about  in  the  following 
manner.  The  wing  is  at  right  angles  to  the  horizon  (x  a;')  at 
c.  It  is  therefore  caught  by  the  air  at  the  point  (2)  because 
of  the  more  or  less  horizontal  travel  of  the  body ;  the  elastic 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  163 

ligaments  and  other  structures  combined  with  the  resistance 
experienced  from  the  air  rotating  the  posterior  or  thin 
margin  of  the  pinion  in  an  upward  direction,  as  shown  at 
defff  and  dfg  of  figs.  84  and  85,  p.  1GO.  The  wing  by 
this  partly  vital  and  partly  mechanical  arrangement  is  rotated 
off  the  wind  in  such  a  manner  as  to  keep  its  dorsal  or  non- 
biting  surface  directed  upwards,  while  its  concave  or  biting 
surface  is  directed  downwards.  •  The  wing,  in  short,  has  its 
planes  so  arranged,  and  its  angles  so  adjusted  to  the  speed 
at  which  it  is  travelling,  that  it  darts  up  a  gradient  like  a 
true  kite,  as  shown  at  cdefgof  figs.  84  and  85,  p.  1GO, 
or  ghi  of  fig.  88,  p.  166.  The  wing  consequently  ele- 
vates and  propels  during  its  ascent  as  well  as  during  its 
descent.  It  is,  in  fact,  a  kite  during  both  the  down  and  up 
strokes.  The  ascent  of  the  wing  is  greatly  assisted  by  the 
fonvard  travel,  and  downward  and  forward  fall  of  the  body. 
This  view  will  be  readily  understood  by  supposing,  what  is 
really  the  case,  that  the  wing  is  more  or  less  fixed  by  the  air 
in  space  at  the  point  indicated  by  2  of  figs.  84  and  85,  p. 
160;  the  body,  the  instant  the  wing  is  fixed,  falling  down- 
wards and  forwards  in  a  curve,  which,  of  course,  is  equivalent 
to  placing  the  wing  above,  and,  so  to  speak,  behind  the  volant 
animal — in  other  words,  to  elevating  the  wing  preparatory  to 
a  second  down  stroke,  as  seen  at  g  of  the  figures  referred  to 
(figs.  84  and  85).  The  ascent  and  descent  of  the  wing  is 
always  very  much  greater  than  that  of  the  body,  from  the  fact 
of  the  pinion  acting  as  a  long  lever.  The  peculiarity  of  the 
wing  consists  in  its  being  a  flexible  lever  which  acts  upon 
yielding  fulcra  (the  air),  the  body  participating  in,  and  to  n 
certain  extent  perpetuating,  the  movements  originally  produced 


Pio.  87. 

by  the  pinion.  The  part  which  the  body  performs  in  flight  is 
indicated  at  fig.  87.  At  a  the  body  is  depressed,  the  wing 
being  elevated  and  ready  to  make  the  down  stroke  at  b.  The 


164  ANIMAL  LOCOMOTION. 

wing  descends  in  the  direction  cd,  but  the  moment  it  begins 
to  descend  the  body  moves  upwards  and  forwards  (see  arrows) 
in  a  curved  line  to  e.  As  the  wing  is  attached  to  the  body 
the  wing  is  made  gradually  to  assume  the  position  /.  The 
body  (e),  it  will  be  observed,  is  now  on  a  higher  level  than 
the  wing  (/) ;  the  under  surface  of  the  latter  being  so  adjusted 
that  it  strikes  upwards  and  forwards  as  a  kite.  It  is  thus 
that  the  wing  sustains  and  propels  during  the  up  stroke.  The 
body  (e)  now  falls  downwards  and  forwards  in  a  curved  line 
to  <7,  and  in  doing  this  it  elevates  or  assists  in  elevating  the 
wing  to  j.  The  pinion  is  a  second  time  depressed  in  the 
direction  k  I,  which  has  the  effect  of  forcing  the  body  along  a 
waved  track  and  in  an  upward  direction  until  it  reaches  the 
point  m.  The  ascent  of  the  body  and  the  descent  of  the* 
wing  take  place  simultaneously  (m  n).  The  body  and  wing, 
are  alternately  above  and  beneath  a  given  line  x  x'. 

A  careful  study  of  figs.  84,  85,  86,  and  87,  pp.  160,  161, 
and  163,  shows  the  great  importance  of  the  twisted  configura- 
tion and  curves  peculiar  to  the  natural  wing.  If  the  wing 
was  not  curved  in  every  direction  it  could  not  be  rolled  on 
and  off  the  wind  during  the  down  and  up  strokes,  as  seen 
more  particularly  at  fig.  87,  p.  163.  This,  however,  is  a  vital 
point  in  progressive  flight.  The  wing  (b)  is  rolled  on  to  the 
wind  in  the  direction  b  a,  its  under  concave  or  biting  surface 
being  crushed  hard  down  with  the  effect  of  elevating  the  body 
to  e.  The  body  falls  to  g,  and  the  wing  (/)  is  rolled  off  the 
wind  in  the  direction  fj,  and  elevated  until  it  assumes  the 
position  j.  The  elevation  of  the  wing  is  effected  partly  by 
the  fall  of  the  body,  partly  by  the  action  of  the  elevator 
muscles  and  elastic  ligaments,  and  partly  by  the  reaction  of 
the  air,  operating  on  its  under  or  concave  biting  surface. 
The  wing  is  therefore  to  a  certain  extent  resting  during  the 
up  stroke. 

The  concavo-convex  form  of  the  wing  is.  admirably  adapted 
for  the  purposes  of  flight.  In  fact,  the  power  which  the  wing 
possesses  of  always  keeping  its  concave  or  under  surface 
directed  downwards  and  forwards  enables  it  to  seize  the  air  at 
every  stage  of  both  the  up  and  down  strokes  so  as  to  supply 
a  persistent  buoyancy.  The  action  of  the  natural  wing  is 
accompanied  by  remarkably  little  slip — the  elasticity  of  the 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  165 

organ,  the  resiliency  of  the  air,  and  the  shortening  and 
elongating  of  the  elastic  ligaments  and  muscles  all  co-operating 
and  reciprocating  in  such  a  manner  that  the  descent  of  the 
wing  elevates  the  body ;  the  descent  of  the  body,  aided  by  the 
reaction  of  the  air  and  the  shortening  of  the  elastic  ligaments 
and  muscles,  elevating  the  wing.  The  wing  during  the  up 
stroke  arcJies  above  the  body  after  the  manner  of  a  parachute, 
and  prevents  the  body  from  falling.  The  sympathy  which 
exists  between  the  parts  of  a  flying  animal  and  the  air  on 
which  it  depends  for  support  and  progress  is  consequently  of 
the  most  intimate  character. 

The  up  stroke  (B,  D  of  figs.  84  and  85,  p.  160),  as  will 
be  seen  from  the  foregoing  account,  is  a  compound  movement 
due  in  some  measure  to  recoil  or  resistance  on  the  part  of  the 
air;  to  the  shortening  of  the  muscles,  elastic  ligaments,  and 
other  vital  structures ;  to  the  elasticity  of  the  wing ;  and  to 
the  falling  of  the  body  in  a  downward  and  forward  direction. 
The  wing  may  be  regarded  as  rotating  during  the  down 
stroke  upon  1  of  figs.  84  and  85,  p.  160,  which  maybe  taken' 
to  represent  the  long  and  short  axes  of  the  wing;  and  during 
the  up  stroke  upon  2,  which  may  be  taken  to  represent  the 
yielding  fulcrum  furnished  by  the  air.  A  second  pulsation  is 
indicated  by  the  numbers  3  and  4  of  the  same  figures  (84, 85). 

The  Wing  ads  upon  yielding  Fulcra. — The  chief  peculiarity 
of  the  wing,  as  has  been  stated,  consists  in  its  being  a  twisted 
flexible  lever  specially  constructed  to  act  upon  yielding 
fulcra  (the  air).  The  points  of  contact  of  the  wing  with  the 
air  are  represented  at  abcdefghijkl  respectively  of 
figs.  84  and  85,  p.  160;  and  the  imaginary  points  of  rotation 
of  the  wing  upon  its  long  and  short  axes  at  1,  2,  3,  and  4  of 
the  same  figures.  The  assumed  points  of  rotation  advance  from 
1  to  3  and  from  2  to  4  (vide  arrows  marked  r  and  s,  fig.  85); 
these  constituting  the  steps  or  pulsations  of  the  wing.  The 
actual  points  of  rotation  correspond  to  the  little  loops  abed 
fghijl  of  fig.  85.  The  wing  descends  at  A  and  C,  and 
ascends  at  B  and  D. 

The  Wing  acts  as  a  true  Kite  loth  during  the  Down  and  Up 
Strokes. — If,  as  I  have  endeavoured  to  explain,  the  wing,  even 
when  elevated  and  depressed  in  a  strictly  vertical  direction, 
inevitably  and  invariably  darts  forward,  it  follows  as  a  con- 


166  ANIMAL  LOCOMOTION. 

sequence  that  the  wing,  as  already  partly  explained,  flies 
forward  as  a  true  kite,  both  during  the  down  and  up  strokes, 
as  shown  akcdefghijklm  of  fig.  88;  and  that  its  under 
concave  or  biting  surface,  in  virtue  of  the  forward  travel 
communicated  to  it  by  the  body  in  motion,  is  closely  applied 
to  the  air,  both  during  its  ascent  and  descent — a  fact  hitherto 
overlooked,  but  one  of  considerable  importance,  as  showing 
how  the  wing  furnishes  a  persistent  buoyancy,  alike  when  it 
rises  and  falls. 


In  fig.  88  the  greater  impulse  communicated  during  the 
down  stroke  is  indicated  by  the  double  dotted  lines.  The 
angle  made  by  the  wing  with  the  horizon  (a  b)  is  constantly 
varying,  as  a  comparison  of  c  with  d,  d  with  e,  e  with  /,  / 
with  g,  g  with  h,  and  h  with  i  will  show ;  these  letters  having 
reference  to  supposed  transverse  sections  of  the  wing.  This 
figure  also  shows  that  the  convex  or  non-biting  surface  of  the 
wing  is  always  directed  upwards,  so  as  to  avoid  unnecessary 
resistance  on  the  part  of  the  air  to  the  wing  during  its  ascent; 
whereas  the  concave  or  biting  surface  is  always  directed  down- 
wards, so  as  to  enable  the  wing  to  contend  successfully  with 
gravity.  • 

JFTiere  the  Kile  formed  by  the  Wing  differs  from  the  Boy's  Kite. 
— The  natural  kite  formed  by  the  wing  differs  from  the  arti- 
ficial kite  only  in  this,  that  the  former  is  capable  of  being 
moved  in  all  its  parts,  and  is  more  or  less  flexible  and  elastic, 
the  latter  being  comparatively  rigid.  The  flexibility  and 
elasticity  of  the  kite  formed  by  the  natural  wing  is  rendered 
necessary  by  the  fact  that  the  wing  is  articulated  or  hinged 
at  its  root ;  its  different  parts  travelling  at  various  degrees  of 
speed  in  proportion  as  they  are  removed  from  the  axis  of 
rotation.  Thus  the  tip  of  the  wing  travels  through  a  much 
greater  space  in  a  given  time  than  a  portion  nearer  the  root. 
If  the  wing  was  not  flexible  and  elastic,  it  would  be  impossible 
to  reverse  it  at  the  end  of  the  up  and  down  strokes,  so  as  to 


PROGRESSION  IN  OR  THROUGH  THE  AIK.  167 

produce  a  continuous  vibration.  The  wing  is  also  practically 
hinged  along  its  anterior  margin,  so  that  the  posterior  margin 
of  the  wing  travels  through  a  greater  space  in  a  given  time 
than  a  portion  nearer  the  anterior  margin  (fig.  80,  p.  149). 
The  compound  rotation  of  the  wing  is  greatly  facilitated  by  the 
wing  being  flexible  and  elastic.  This  causes  the  pinion  to  twist 
upon  its  long  axis  during  its  vibration,  as  already  stated.  The 
twisting  is  partly  a  vital,  and  partly  a  mechanical  act ;  that 
is,  it  is  occasioned  in  part  by  the  action  of  the  muscles,  in  part 
by  the  reaction  of  the  air.  and  in  part  by  the  greater  momen- 
tum acquired  by  the  tip  and  posterior  margin  of  the  wing, 
as  compared  with  the  root  and  anterior  margin;  the  speed 
acquired  by  the  tip  and  posterior  margin  causing  them  to 
reverse  always  subsequently  to  the  root  and  anterior  margin, 
which  has  the  effect  of  throwing  the  anterior  and  posterior 
margins  of  the  wing  into  figure-of-8  curves.  It  is  in  this  way 
that  the  posterior  margin  of  the  outer  portion  of  the  wing  is 
made  to  incline  forwards  at  the  end  of  the  down  stroke,  when 
the  anterior  margin  is  inclined  backwards;  the  posterior 
margin  of  the  outer  portion  of  the  wing  being  made  to 
incline  backwards  at  the-  end  of  the  up  stroke,  when  a  cor- 
responding portion  of  the  anterior  margin  is  inclined  forwards 
(figs.  69  and  70,  g,a,  p.  141 ;  fig.  86,;,/,  p.  161). 

The  Angles  formed  by  the  Wing  during  its  Vibrations. — Not 
the  least  interesting  feature  of  the  compound  rotation  of  the 
wing — of  the  varying  degrees  of  speed  attained  by  its  different 
parts — and  of  the  twisting  or  plaiting  of  the  posterior  margin 
around  the  anterior, — is  the  great  variety  of  kite-like  surfaces 
developed  upon  its  dorsal  and  ventral  aspects.  Thus  the  tip 
of  the  wing  forms  a  kite  which  is  inclined  upwards,  forwards, 
and  outwards,  while  the  root  forms  a  kite  which  is  inclined 
upwards,  forwards,  and  inwards.  The  angles  made  by  the 
tip  and  outer  portions  of  the  wing  with  the  horizon  are  less 
than  those  made  by  the  body  or  central  part  of  the  wing,  and 
those  made  by  the  body  or  central  part  less  than  those  made 
by  the  root  and  inner  portions.  The  angle  of  inclination 
peculiar  to  any  portion  of  the  wing  increases  as  the  speed 
peculiar  to  said  portion  decreases,  and  vice  versd.  The  wing 
is  consequently  mechanically  perfect ;  the  angles  made  by  its 


168  ANIMAL  LOCOMOTION. 

several  parts  with  the  horizon  being  accurately  adjusted  to 
the  speed  attained  by  its  different  portions  during  its  travel 
to  and  fro.  From  this  it  follows  that  the  air  set  in  motion 
by  one  part  of  the  wing  is  seized  upon  and  utilized  by 
another;  the  inner  and  anterior  portions  of  the  wing  supply- 
ing, as  it  were,  currents  for  the  outer  and  posterior  portions. 
This  results  from  the  wing  always  forcing  the  air  outwards 
and  backwards.  These  statements  admit  of  direct  proof,  and 
I  have  frequently  satisfied  myself  of  their  exactitude  by  ex- 
periments made  with  natural  and  artificial  wings. 

In  the  bat  and  bird,  the  twisting  of  the  wing  upon  its  long 
axis  is  more  of  a  vital  and  less  of  a  mechanical  act  than  in 
the  insect ;  the  muscles  which  regulate  the  vibration  of  the 
pinion  in  the  former  (bat  and  bird),  extending  quite  to  the 
tip  of  the  wing  (fig.  95,  p.  175  ;  figs.  82  and  83,  p.  158). 

The  Body  and  Wings  move  in  opposite  Curves. — I  have  stated 
that  the  wing  advances  in  a  waved  line,  as  shown  at  a  c  e  g  i 
of  fig.  81,  p.  157;  and  similar  remarks  are  to  be  made  of 
the  body  as  indicated  at  1,  2,  3,  4,  5  of  that  figure.  Thus, 
when  the  wing  descends  in  the  curved  line  a  c,  it  elevates 
the  body  in  a  corresponding  but  minor  curved  line,  as  at 
1,  2 ;  when,  on  the  other  hand,  the  wing  ascends  in  the 
curved  line  c  e,  the  body  descends  in  a  corresponding  but 
smaller  curved  line  (2,  3),  and  so  on  ad  infinitum.  The  un- 
dulations made  by  the  body  are  so  trifling  when  compared 
with  those  made  by  the  wing,  that  they  are  apt  to  be 
overlooked.  They  are,  however,  deserving  of  attention,  as 
they  exercise  an  important  influence  on  the  undulations  made 
by  the  wing;  the  body  and  wing  swinging  forward  alternately, 
the  one  rising  when  the  other  is  falling,  and  vice  versa. 
Flight  may  be  regarded  as  the  resultant  of  three  forces  : — the 
muscular  and  elastic  force,  residing  in  the  wing,  which  causes 
the  pinion  to  act  as  a  true  kite,  both  during  the  down  and  up 
strokes;  the  weight  of  the  body,  which  becomes  a  force  the 
instant  the  trunk  is  lifted  from  the  ground,  from  its  tendency 
to  fall  downwards  and  forwards ;  and  the  recoil  obtained  from 
the,  air  by  the  rapid  action  of  the  wing.  These  three  forces 
may  be  said  to  be  active  and  passive  by  turns. 

When  a  bird  rises  from  the  ground  it  runs  for  a  short 


PROGRESSION  IN  OR  THROUGH  THE  AIR.      169 

distance,  or  throws  its  body  into  the  air  by  a  sudden  leap, 
the  wings  being  simultaneously  elevated.  When  the  body  is 
fairly  off  the  ground,  the  wings  are  made  to  descend  with 
great  vigour,  and  by  their  action  to  continue  the  upward 
impulse  secured  by  the  preliminary  run  or  leap.  The  body 
then  falls  in  a  curve  downwards  and  forwards ;  the  wings, 
partly  by  the  fall  of  the  body,  partly  by  the  reaction  of  the 
air  on  their  under  surface,  and  partly  by  the  shortening  of 
the  elevator  muscles  and  elastic  ligaments,  being  placed  above 
and  to  some  extent  behind  the  bird — in  other  words,  elevated. 
The  second  down  stroke  is  now  given,  and  the  wings  again 
elevated  as  explained,  and  so  on  in  endless  succession ;  the 
body  falling  when  the  wings  are  being  elevated,  and  vice 
versa  (fig.  81,  p.  157).  When  a  long- winged  oceanic  bird 
rises  from  the  sea,  it  uses  the  tips  of  its  wings  as  levers  for 
forcing  the  body  up ;  the  points  of  the  pinions  suffering  no 
injury  from  being  brought  violently  in  contact  with  the 
water.  A  bird  cannot  be  said  to  be  flying  until  the  trunk  is 
swinging  forward  in  space  and  taking  part  in  the  movement. 
The  hawk,  when  fixed  in  the  air  over  its  quarry,  is  simply 
supporting  itself.  To  fly,  in  the  proper  acceptation  of  the 
term,  implies  to  support  and  propel.  This  constitutes  the 
difference  between  a  bird  and  a  balloon.  The  bird  can 
elevate  and  carry  itself  forward,  the  balloon  can  simply  elevate 
itself,  and  must  rise  and  fall  in  a  straight  line  in  the  absence 
of  currents.  When  the  gannet  throws  itself  from  a  cliff,  the 
inertia  of  the  trunk  at  once  comes  into  play,  and  relieves  the 
bird  from  those  herculean  exertions  required  to  raise  it  from 
the  water  when  it  is  once  fairly  settled  thereon.  A  swallow 
dropping  from  the  eaves  of  a  house,  or  a  bat  from  a  tower, 
afford  illustrations  of  the  same  principle.  Many  insects 
launch  themselves  into  space  prior  to  flight.  Some,  however, 
do  not.  Thus  the  blow-fly  can  rise  from  a  level  surface  when 
its  legs  are  removed.  This  is  accounted  for  by  the  greater 
amplitude  and  more  horizontal  play  of  the  insect's  wing  as 
compared  with  that  of  the  bat  and  bird,  and  likewise  by  the 
remarkable  reciprocating  power  which  the  insect  wing  pos- 
sesses when  the  body  of  the  insect  is  not  moving  forwards 
(figs.  67,  68,  69,  and  70  p.  141).  When  a  beetle  attempts 


1  70  ANIMAL  LOCOMOTION. 

to  fly  from  the  hand,  it  extends  its  front  legs  and  flexes 
the  back  ones,  and  tilts  its  head  and  thorax  upwards,  so 
as  exactly  to  resemble  a  horse  in  the  act  of  rising  from  the 
ground.  This  preliminary  over,  whirr  go  its  wings  with  im- 
mense velocity,  and  in  an  almost  horizontal  direction,  the 
body  being  inclined  more  or  less  vertically.  The  insect  rises 
very  slowly,  and  often  requires  to  make  several  attempts 
before  it  succeeds  in  launching  itself  into  the  air.  I  could 
never  detect  any  pressure  communicated  to  the  hand  when 
the  insect  was  leaving  it,  from  which  I  infer  that  it  does  not 
leap  into  the  air.  The  bees,  I  am  disposed  to  believe,  also 
rise  without  anything  in  the  form  of  a  leap  or  spring.  I 
have  often  watched  them  leaving  the  petals  of  flowers,  and 
they  always  appeared  to  me  to  elevate  themselves  by  the  steady 
play  of  their  wings,  which  was  the  more  necessary,  as  the  sur- 
face from  which  they  rose  was  in  many  cases  a  yielding  surface. 

THE  WINGS  OF  INSECTS,  BATS,  AND  BIRDS. 

Elytra  or  Wing-cases,  Membranous  Wings — their  shape  and 
uses. — The  wings  of  insects  consist  either  of  one  or  two  pairs. 
When  two  pairs  are  present,  they  are  divided  into  an  ante- 
rior or  upper  pair,  and  a  posterior  or  under  pair.  In  some 
instances  the  anterior  pair  are  greatly  modified,  and  present 
a  corneous  condition.  When  so  modified,  they  cover  the 
under  wings  when  the  insect  is  reposing,  and  have  from 
this  circumstance  been  named  elytra,  from  the  Greek  eXvrpov, 
a  sheath.  The  anterior  wings  are  dense,  rigid,  and  opaque 
in  the  beetles  (fig.  89,  r) ;  solid  in  one  part  and  membran- 
aceous  in  another  in  the  water-bugs  (fig.  90,  r)  j  more  or  less 
membranous  throughout  in  the  grasshoppers ;  and  completely 
membranous  in  the  dragon-flies  (fig.  91,  e  e,  p.  172).  The 
superior  or  upper  wings  are  inclined  at  a  certain  angle  when 
extended,  and  are  indirectly  connected  with  flight  in  the 
beetles,  water-bugs,  and  grasshoppers.  They  are  actively 
engaged  in  this  function  in  the  dragon-flies  and  butterflies. 
The  elytra  or  anterior  wings  are  frequently  employed  as  sus- 
tainers  or  gliders  in  flight,1  the  posterior  wings  acting  more 

1  That  the  elytra  take  part  in  flight  is  proved  by  this,  that  when  they 
are  removed,  flight  is  in  many  cases  destroyed. 


PROGRESSION  IN  OR  THKOUGH  THE  AIR. 


171 


particularly  as  elevators  and  propellers.    In  such  cases  the  elytra 
are  twisted  upon  themselves  after  the  manner  of  wings. 


FIG.  89. 


Pro.  90. 

FIG.  89. — the  Centaur  Beetle  (Augwoma  centaurus),  seen  from  above.  Shows 
elytra  (r)  and  membranous  wings  (e)  in  the  extended  state.  The  nervures 
are  arranged  and  jointed  in  such  a  manner  that  the  membranous  wings  can 
be  folded  (t)  transversely  across  the  back  beneath  the  elytra  during  repose. 
When  so  folded,  the  anterior  or  thick  margins  of  the  membranous  wings  are 
directed  outwards  and  slightly  downwards,  the  posterior  or  thin  margins  in- 
wards and  slightly  upwards.  During  extension  the  positions  of  the  margins 
are  reversed  by  the  wings  twisting  and  rotating  upon  their  long  axes,  the 
anterior  margins,  as  in  bats  and  birds,  being  directed  upwards  and  forwards, 
and  making  a  very  decided  angle  with  the  horizon.  The  wings  in  the  beetles 
are  insignificantly  small  when  compared  with  the  area  of  the  body.  They  are, 
moreover,  finely  twisted  upon  themselves,  and  possess  great  power  as  pro- 
pellers  and  elevators. — Original. 

FIG.  90. — The  Water-Bug  (Genus  belost&ma).  In  this  insect  the  superior  wings 
(elytra  or  wing  covers  r)  are  semi-membranous.  They  are  geared  to  the 
membranous  or  under  wings  [a)  by  a  book,  the  two  acting  together  in  flight. 
"When  so  geared  the  upper  and  under  wings  are  delicately  curved  and 
twisted.  They  moreover  taper  from  within  outwards,  and  from  before  back- 
wards.— Original. 


172  ANIMAL  LOCOMOTION. 

The  wings  of  insects  present  different  degrees  of  opacity — 
those  of  the  moths  and  butterflies  being  non -transparent; 
those  of  the  dragon-flies,  bees,  and  common  flies  presenting  a 
delicate,  filmy,  gossamer-like  appearance.  The  wings  in  every 
case  are  composed  of  a  duplicature  of  the  integument  or  in- 


Fio.  91.— The  Dragon-fly  (Petnlura  gigantea).  In  this  insect  the  wings  are 
finely  curved  and  delicately  transparent,  the  nervnres  being  most  strongly 
developed  at  the  roots  of  the  wings  and  along  the  anterior  margins  (e  e,  //), 
and  least  so  at  the  tips  (6  6),  and  along  the  posterior  margins  (a  a).  The 
anterior  pair  (e  e)  are  analogous  in  every  respect  to  the  posterior  (//).  Both 
make  a  certain  angle  with  the  horizon,  the  anterior  pair(ee),  which  are  prin- 
cipally used  as  elevators,  making  a  smaller  angle  than  the  posterior  pair 
(//),  which  are  used  as  drivers.  The  wings  of  the  dragon-fly  make  the  proper 
angles  for  flight  even  in  repose,  so  that  the  insect  can  take  to  wing  instantly. 
The  insect  flies  with  astonishing  velocity. — Original. 

vesting  membrane,  and  are  strengthened  in  various  directions 
by  a  system  of  hollow,  horny  tubes,  known  to  entomologists 
as  the  neurae  or  nervures.  The  nervures  taper  towards  the 
extremity  of  the  wing,  and  are  strongest  towards  its  root  and 
anterior  margin,  where  they  supply  the  place  of  the  arm  in 
bats  and  birds.  They  are  variously  arranged.  In  the  beetles 
they  pursue  a  somewhat  longitudinal  course,  and  are  jointed  to 
admit  of  the  wing  being  folded  up  transversely  beneath  the 
elytra.1  In  the  locusts  the  nervures  diverge  from  a  common 
centre,  after  the  manner  of  a  fan,  so  that  by  their  aid  the  wing 
is  crushed  up  or  expanded  as  required ;  whilst  in  the  dragon-fly, 

1  The  wings  of  the  May-fly  are  folded  longitudinally  and  transversely,  so 
that  they  are  crumpled  up  into  little  squares. 


PEOGRESSION  IN  OR  THROUGH  THI!  AIR.  173 

where  no  folding  is  requisite,  they  form  an  exquisitely  reti- 
culated structure.  The  nervures,  it  may  be  remarked,  are 
strongest  in  the  beetles,  where  the  body  is  heavy  and  the 
wing  small.  They  decrease  in  thickness  as  those  conditions 
are  reversed,  and  entirely  disappear  in  the  minute  chalcis  and 
psilus.1  The  function  of  the  nervures  is  not  ascertained ;  but 
as  they  contain  spiral  vessels  which  apparently  communicate 
with  the  tracheae  of  the  trunk,  some  have  regarded  them  as 
being  connected  with  the  respiratory  system;  whilst  others 
have  looked  upon  them  as  the  receptacles  of  a  subtle  fluid, 
which  the  insect  can  -introduce  and  withdraw  at  pleasure  to 
obtain  the  requisite  degree  of  expansion  and  tension  in  the 
wing.  Neither  hypothesis  is  satisfactory,  as  respiration  and 
flight  can  be  performed  in  their  absence.  They  appear  to 
me,  when  present,  rather  to  act  as  mechanical  stays  or 
stretchers,  in  virtue  of  their  rigidity  and  elasticity  alone, — 
their  arrangement  being  such  that  they  admit  of  the  wing 
being  folded  in  various  directions,  if  necessary,  during  flexion, 
and  give  it  the  requisite  degree  of  firmness  during  extension. 
They  are,  therefore,  in  every  respect  analogous  to  the  skeleton 
of  the  wing  in  the  bat  and  bird.  In  those  wings  which, 
during  the  period  of  repose,  are  folded  up  beneath  the  elytra, 
the  mere  extension  of  the  wing  in  the  dead  insect,  where  no 
injection  of  fluid  can  occur,  causes  the  nervures  to  fall  into 
position,  and  the  membranous  portions  of  the  wing  to  unfurl 
or  roll  out  precisely  as  in  the  living  insect,  and  as  happens  in 
the  bat  and  bird.  This  result  is  obtained  by  the  spiral  arrange- 
ment of  the  nervures  at  the  root  of  the  wing;  the  anterior  ner- 
•  vure  occupying  a  higher  position  than  that  further  back,  as  in 
the  leaves  of  a  fan.  The  spiral  arrangement  occurring  at 
the  root  extends  also  to  the  margins,  so  that  wings  which  fold 
up  or  close,  as  well  as  those  which  do  not,  are  twisted  upon 
themselves,  and  present  a  certain  degree  of  convexity  on  their 
superior  or  upper  surface,  and  a  corresponding  concavity  on 
their  inferior  or  under  surface;  their  free  edges  supplying 
those  fine  curves  which  act  with  such  efficacy  upon  the  air, 
in  obtaining  the  maximum  of  resistance  and  the  minimum 
of  displacement;  or  what  is  the  same  thing,  the  maximum 
of  support  with  the  minimum  of  slip  (figs.  92  and  93). 
1  Kirby  and  Spence,  vol.  ii.  5th  eel.,  p.  352. 


174 


ANIMAL  LOCOMOTION. 


The  wings  of  insects  can  be  made  to  oscillate  within  given 
areas  anteriorly,  posteriorly,  or  centrally  with  regard  to  the 
plane  of  the  body;  or  in  intermediate  positions  with  regard  to 
it  and  a  perpendicular  line.  The  wing  or  wings  of  the  one 


FIG.  93. 

FIG.  92.— Right  wing  of  Beetle  (Goliathus  mican»\  dorsal  surface.  This  wing 
somewhat  resembles  the  kestrel's  (fig.  61,  p.  136)  in  shape.  It  has  an  ante- 
rior thick  margin,  d  e  f,  and  a  posterior  thin  one,  b  a-  c.  Strong  nervures 
run  along  the  anterior  margin  (d),  until  they  reach  the  joint  («).  where  the 
wing  folds  upon  itself  during  repose.  Here  the  nervures  split  up  and  di- 
varicate and  gradually  become  smaller  and  smaller  until  they  reach  the  ex- 
tremity of  the  wing  (/)  and  the  posterior  or  thin  margin  (b);  other  ner- 
vures radiate  in  graceful  curves  from  the  root  of  the  wing.  These  also 
become  finer  as  they  reach  the  posterior  or  thin  margin  (c  a),  r,  Root  of 
the  wing  with  its  complex  compound  joint.  The  wing  of  the  beetle  bears 
a  certain  analogy  to  that  of  the  bat,  the  nervures  running  along  the  anterior 
margin  (d)  of  the  wing,  resembling  the  humerus  and  forearm  of  the  bat  (fig. 
94,  d,  p.  175),  the  joint  of  the  beetle's  wing  (e)  corresponding  to  the  carpal  or 
wrist-joint  of  the  bat's  wing  (fig.  94,  e),  the  terminal  or  distal  nervures  of  the 
beetle  (/  b)  to  the  phalanges  of  the  bat  (fig.  94,  /  b).  The  parts  marked  fb 
may  in  both  instances  be  likened  to  the  primary  feathers  of  the  bird,  that 
marked  a  to  the  secondary  feathers,  and  c  to  the  tertiary  feathers.  In  the 
wings  of  the  beetle  and  bat  no  air  can  possibly  escape  through  them  during  the 
return  or  up  stroke.— Original. 

FIG.  93.— Right  wing  of  the  Beetle  (Goliathus  micanft).  as  seen  from  behind 
and  from  beneath.  When  so  viewed,  the  anterior  or  thick  margin  (d  f)  and 
the  posterior  or  thin  margin  (6  *  c)  are  arranged  in  different  planes,  and  form 
a  true  helix  or  screw.  Compare  with  figs.  95  and  97.— Original. 

side  can  likewise  be  made  to  move  independently  of  those  of 
the  opposite  side,  so  that  the  centre  of  gravity,  which,  in 
insects,  bats,  and  birds,  is  suspended,  is  not  disturbed  in  the 
endless  evolutions  involved  in  ascending,  descending,  and 
wheeling.  The  centre  of  gravity  varies  in  insects  according 
to  the  shape  of  the  body,  the  length  and  shape  of  the 
limbs  and  antennae,  and  the  position,  shape,  and  size  of  the 


PROGRESSION  IN  OR  THROUGH  THE  AIR. 


175 


pinions.  It  is  corrected  in  some  by  curving  the  body,  in 
others  by  bending  or  straightening  the  limbs  and  antennae, 
but  principally  in  all  by  the  judicious  play  of  the  wings 
themselves. 

The  wing  of  the  bat  and  bird,  like  that  of  the  insect,  is 
concavo-convex,  and  more  or  less  twisted  upon  itself  (figs. 
94,  95,  96,  and  97). 


margin,  supported  by  the  remaining  phalanges,  by  the  side  of  the  body,  and 
by  the  foot.  —  Original. 
Fio.  95.— Right  wing  of  the  Bat  (Phyllorhina  gracilis),  as  seen  from  behind  and 
from  beneath.  When  so  regarded,  the  anterior  or  thick  margin  (rf /)  of  the 
wing  displays  different  curves  from  those  seen  on  the  posterior  or  thin  mar- 
gin (ft  c) ;  the  anterior  and  posterior  margins  being  arranged  in  different 
planes,  as  in  the  blade  of  a  screw  propeller. — Original. 

The  twisting  is  in  a  great  measure  owing  to  the  manner  in 
which  the  bones  of  the  wing  are  twisted  upon  themselves,  and 
the  spiral  nature  of  their  articular  surfaces ;  the  long  axes  of 
the  joints  always  intersecting  each  other  at  nearly  right  angles. 
As  a  result  of  this  disposition  of  the  articular  surfaces,  the 
wing  is  shot  out  or  extended,  and  retracted  or  flexed  in  a 
variable  plane,  the  bones  of  the  wing  rotating  in  the  direction 
of  their  length  during  either  movement.  This  secondary 
action,  or  the  revolving  of  the  component  bones  upon  their 
own  axes,  is  of  the  greatest  importance  in  the  movements  of 
the  wing,  as  it  communicates  to  the  hand  and  forearm,  and 


176 


ANIMAL  LOCOMOTION. 


consequently  to  the  membrane  or  feathers  which  they  bear, 
the  precise  angles  necessary  for  flight.  It,  in  fact,  insures 
that  the  wing,  and  the  curtain,  sail,  or  fringe  of  the  wing 
shall  be  screwed  into  and  down  upon  the  air  in  extension, 
and  unscrewed  or  withdrawn  from  it  during  flexion.  The 
wing  of  the  bat  and  bird  may  therefore  be  compared  to  a 
huge  gimlet  or  auger,  the  axis  of  the  gimlet  representing  the 
bones  of  the  wing  ;  the  flanges  or  spiral  thread  of  the  gimlet 
the  frenum  or  sail  (figs.  95  and  97). 


Fro.  97. 

Fio.  96.— Right  wing  of  the  Red-legged  Partridge  (Perdix  rubra),  dorsal 
aspect.  Shows  extreme  example  of  short  rounded  wing  ;  contrast  with  the 
wing  of  the  albatross  (fig.  62,  p.  137),  which  furnishes  an  extreme  example 
of  the  long  ribbon-shaped  wing  ;  d  e  f,  anterior  margin  ;  6  a  c,  posterior 
ditto,  consisting  of  primary  (6),  secondary  (a),  and  tertiary  (c)  feathers, 
with  their  respective  coverts  and  subcoverts ;  the  whole  overlapping  and 
mutually  supporting  each  other.  This  wing,  like  the  kestrel's  (fig.  61,  p. 
136),  was  drawn  from  a  specimen  held  against  the  light,  the  object  being  to 
display  the  mutual  relation  of  the  feathers  to  each  other,  and  how  the 
feathers  overlap. — Original. 

FIG.  97. — Right  wing  of  Red-legged  Partridge  (Perdix  nibra),  seen  from  be- 
hind and  from  beneath,  as  in  the  beetle  (fig.  93)  and  bat  (fig.  95).  The  same 
lettering  and  explanation  does  for  all  three. — Original. 


THE  WINGS  OF  BATS. 

The  Bones  of  the  Wing  of  the  Bat — the  spiral  configuration 
of  tJmr  articular  surfaces. — The  bones  of  the  arm  and  hand 
are  especially  deserving  of  attention.  The  humerus  (fig. 
17,  r,  p.  36)  is  short  and  powerful,  and  twisted  upon  itself 
to  the  extent  of  something  less  than  a  quarter  of  a  turn. 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  177 

As  a  consequence,  the  long  axis  of  the  shoulder-joint  is  nearly 
at  right  angles  to  that  of  the  elbow-joint.  Similar  remarks 
may  be  made  regarding  the  radius  (the  principal  bone  of 
the  forearm)  (d),  and  the  second  and  third  metacarpal  bones  ' 
with  their  phalanges  (e  /),  all  of  which  are  greatly  elongated, 
and  give  strength  and  rigidity  to  the  anterior  or  thick 
margin  of  the  wing.  The  articular  surfaces  of  the  bones 
alluded  to,  as  well  as  of  the  other  bones  of  the  hand,  are 
spirally  disposed  with  reference  to  each  other,  the  long  axes 
of  the  joints  intersecting  at  nearly  right  angles.  The  object 
of  this  arrangement  is  particularly  evident  when  the  wing  of 
the  living  bat,  or  of  one  recently  dead,  is  extended  and  flexed 
as  in  flight. 

In  the  flexed  state  the  wing  is  greatly  reduced  in  size,  its 
under  surface  being  nearly  parallel  with  the  plane  of  progres- 
sion. When  the  wing  is  fully  extended  its  under  surface 
makes  a  certain  angle  with  the  horizon,  the  wing  being  then 
in  a  position  to  give  the  down  stroke,  which  is  delivered 
downwards  and  forwards,  as  in  the  insect.  When  extension 
takes  place  the  elbow-joint  is  depressed  and  carried  forwards, 
the  wrist  elevated  and  carried  backwards,  the  metacarpo- 
phalangeal  joints  lowered  and  inclined  forwards,  and  the 
distal  phalangeal  joints  slightly  raised  and  carried  backwards. 
The  movement  of  the  bat's  wing  in  extension  is  consequently 
a  spiral  one,  the  spiral  running  alternately  from  below  up- 
wards and  forwards,  and  from  above  downwards  and  back- 
wards (compare  with  fig.  79,  p.  147).  As  the  bones  of  the 
arm,  forearm,  and  hand  rotate  on  their  axes  during  the  exten- 
sile act,  it  follows  that  the  posterior  or  thin  margin  of  the 
wing  is  rotated  in  a  downward  direction  (the  anterior  or 
thick  one  being  rotated  -in  an  opposite  direction)  until  the 
wing  makes  an  angle  of  something  like  30°  with  the  horizon, 
which,  as  I  have  already  endeavoured  to  show,  is  the  greatest 
angle  made  by  the  wing  in  flight.  The  action  of  the  bat's 
wing  at  the  shoulder  is  particularly  free,  partly  because  the 
shoulder-joint  is  universal  in  its  nature,  and  partly  because  the 
scapula  participates  in  the  movements  of  this  region.  The 
freedom  of  action  referred  to  enables  the  bat  not  only  to 
rotate  and  twist  its  wing  as  a  whole,  with  a  view  to  dimin- 


178  ANIMAL  LOCOMOTION. 

ishing  and  increasing  the  angle  which  its  under  surface  makes 
with  the  horizon,  but  to  elevate  and  depress  the  wing,  and 
move  it  in  a  forward  and  backward  direction.  The  rotatory 
or  twisting  movement  of  the  wing  is  an  essential  feature  in 
flight,  as  it  enables  the  bat  (and  this  holds  true  also  of  the 
insect  and  bird)  to  balance  itself  with  the  utmost  exactitude, 
and  to  change  its  position  and  centre  of  gravity  with  mar- 
vellous dexterity.  The  movements  of  the  shoulder-joint  are 
restrained  within  certain  limits  by  a  system  of  check-ligaments, 
and  by  the  coracoid  and  acromian  processes  of  the  scapula. 
The  wing  is  recovered  or  flexed  by  the  action  of  elastic  liga- 
ments which  extend  between  the  shoulder,  elbow,  and  wrist. 
Certain  elastic  and  fibrous  structures  situated  between  the 
fingers  and  in  the  substance  of  the  wing  generally  take  part 
in  flexion.  The  bat  flies  with  great  ease  and  for  lengthened 
periods.  Its  flight  is  remarkable  for  its  softness,  in  which 
respect  it  surpasses  the  owl  and  the  other  nocturnal  birds. 
The  action  of  the  wing  of  the  bat,  and  the  movements  of 
its  component  bones,  are  essentially  the  same  as  in  the  bird. 

THE  WINGS  OF  BIRDS. 

The  Bones  of  the  Wing  of  the  Bird — their  Articular  Sur- 
faces, Movements,  etc. — The  humerus,  or  arm-bone  of  the 
wing,  is  supported  by  three  of  the  trunk-bones,  viz.  the 
scapula  or  shoulder-blade,  the  clavicle  or  collar-bone,  also 
called  the  furculum,1  and  the  coracoid  bone, — these  three 
converging  to  form  a  point  d'appui,  or  centre  of  support  for 
the  head  of  the  humerus,  which  is  received  in  facettes  or 
depressions  situated  on  the  scapula  and  coracoid.  In  order 
that  the  wing  may  have  an  almost  -unlimited  range  of  motion, 
and  be  wielded  after  the  manner  of  a  flail,  it  is  articulated  to 
the  trunk  by  a  somewhat  lax  universal  joint,  which  permits 

1  The  furcula  are  usually  united  to  the  anterior  part  of  the  sternum  by 
ligament ;  but  in  birds  of  powerful  flight,  where  the  wings  are  habitually 
extended  for  gliding  and  sailing,  as  in  the  frigate-bird,  the  union  is  osseous  in 
its  nature.  "In  the  frigate-bird  the  furcula  are  likewise  anchyloseu  with 
the  coracoid  bones." — Comp.  Anat.  and  Phys.  of  Vertebrates,  by  Prof.  Owen, 
vol.  ii.  p.  66. 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  179 

vertical,  horizontal,  and  intermediate  movements.1  The  long 
axis  of  the  joint  is  directed  vertically;  the  joint  itself  some- 
what backwards.  It  is  otherwise  with  the  elbow-joint,  which 
is  turned  forwards,  and  has  its  long  axis  directed  horizontally, 
from  the  fact  that  the  humerus  is  twisted  upon  itself  to  the 
extent  of  nearly  a  quarter  of  a  turn.  The  elbow-joint  is 
decidedly  spiral  in  its  nature,  its  long  axis  intersecting  that  of 
the  shoulder-joint  at  nearly  right  angles.  The  humerus 
articulates  at  the  elbow  with  two  bones,  the  radius  and  the 
ulna,  the  former  of  which  is  pushed  from  the  humerus,  while 
the  other  is  drawn  towards  it  during  extension,  the  reverse 
occurring  during  flexion.  Both  bones,  moreover,  while  those 
movements  are  taking  place,  Tevolve  to  a  greater  or  less  extent 
upon  their  own  axes.  The  bones  of  the  forearm  articulate  at 
the  wrist  with  the  carpal  bones,  which  being  spirally  arranged, 
and  placed  obliquely  between  them  and  the  metacarpal  bones, 
transmit  the  motions  to  the  latter  in  a  curved  direction.  The 
long  axis  of  the  wrist-joint  is,  as  nearly  as  may  be,  at  right 
angles  to  that  of  the  elbow-joint,  and  more  or  less  parallel 
with  that  of  the  shoulder.  The  metacarpal  or  hand-bones, 
and  the  phalanges  or  finger-bones  are  more  or  less  fused 
together,  the  better  to  support  the  great  primary  feathers,  on 
the  efficiency  of  which  flight  mainly  depends.  They  are 
articulated  to  each  other  by  double  hinge-joints,  the  long  axes 
of  which  are  nearly  at  right  angles  to  each  other. 

As  a  result  of  this  disposition  of  the  articular  surfaces,  the 
wing  is  shot  out  or  extended  and  retracted  or  flexed  in  a 
variable  plane,  the  bones  composing  the"  wing,  particularly 
those  of  the  forearm,  rotating  on  their  axes  during  either 
movement. 

This  secondary  action,  or  the  revolving  of  the  component 
bones  upon  their  own  axes,  is  of  the  greatest  importance  in 
the  movements  of  the  wing,  as  it  communicates  to  the  hand 

1  "  The  os  humeri,  or  bone  of  the  arm,  is  articulated  by  a  small  rounded 
surface  to  a  corresponding  cavity  formed  between  the  coracoid  bone  and  the 
scapula,  in  such  a  manner  as  to  allow  great  freedom  of  motion." — Macgillivray's 
Brit.  Birds,  vol.  i.  p.  33. 

"  The  arm  is  articulated  to  the  trunk  by  a  ball-and-socket  joint,  permitting 
all  the  freedom  of  motion  necessary  for  flight." — Cyc.  of  Anat.  and  Phys., 
vol.  iii.  p.  424. 


180  ANIMAL  LOCOMOTION. 

and  forearm,  and  consequently  to  the  primary  and  secondary 
feathers  which  they  bear,  the  precise  angles  necessary  for 
flight ;  it  in  fact  insures  that  the  wing,  and  the  curtain  or 
fringe  of  the  wing  which  the  primary  and  secondary  feathers 
form,  shall  be  screwed  into  and  down  upon  the  air  in  ex- 
tension, and  unscrewed  or  withdrawn  from  it  during  flexion. 
The  whig  of  the  bird  may  therefore  be  compared  to  a  huge 
gimlet  or  auger;  the  axis  of  the  gimlet  representing  the 
bones  of  the  wing,  the  flanges  or  spiral  thread  of  the  gimlet 
the  primary  and  secondary  feathers  (fig.  63,  p.  138,  and  fig. 
97,  p.  176). 

Traces  of  Design  in  the  Wing  of  the  Bird — the  arrangement  of 
tlie  Primary,  Secondary,  and  Tertiary  Feathers,  etc. — There  are 
few  things  in  nature  more  admirably  constructed  than  the 
wing  of  the  bird,  and  perhaps  none  where  design  can  be  more 
readily  traced.  Its  great  strength  and  extreme  lightness,  the 
manner  in  which  it  closes  up  or  folds  during  flexion,  and 
opens  out  or  expands  during  extension,  as  well  as  the  manner 
in  which  the  feathers  are  strung  together  and  overlap  each 
other  in  divers  directions  to  produce  at  one  time  a  solid 
resisting  surface,  and  at  another  an  interrupted  and  compara- 
tively non-resisting  one,  present  a  degree  of  fitness  to  which 
the  mind  must  necessarily  revert  with  pleasure.  If  the 
feathers  of  the  wing  only  are  contemplated,  they  may  be  con- 
veniently divided  into  three  sets  of  three  each  (on  both  sides 
of  the  wing) — an  upper  or  dorsal  set  (fig.  61,  d,  e,f,  p.  1 36),  a 
lower  or  ventral  set  (c,  a,  &),  and  one  which  is  intermediate. 
This  division  is  intended  to  refer  the  feathers  to  the  bones  of 
the  arm,  forearm,  and  hand,  but  is  more  or  less  arbitrary  in 
its  nature.  The  lower  set  or  tier  consists  of  the  primary  (b), 
secondary  (a),  and  tertiary  (c)  feathers,  strung  together  by 
fibrous  structures  in  such  a  way  that  they  move  in  an  out- 
ward or  inward  direction,  or  turn  upon  their  axes,  at  precisely 
the  same  instant  of  time, — the  middle  and  upper  sets  of 
feathers,  which  overlap  the  primary,  secondary,  and  tertiary 
ones,  constituting  what  are  called  the  "  coverts  "  and  "  sub- 
coverts."  The  primary  or  rowing  feathers  are  the  longest  and 
strongest  (b),  the  secondaries  (a)  next,  and  the  tertiaries  third 
(c).  The  tertiaries,  however,  are  occasionally  longer  than  the 


PROGRESSION  IN  OR  THROUGH  THE  AIR. 


181 


secondaries.     The  tertiary,  secondary,  and  primary  feathers 
increase  in  strength  from  within  outwards,  i.e.  from  the  body 


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of  wing-coverts.     This  arrangement  is  necessary,  because  the 


182  ANIMAL  LOCOMOTION. 

strain  on  the  feathers  during  flight  increases  in  proportion  to 
their  distance  from  the  trunk. 

The  manner  in  which  the  roots  of  the  primary,  secondary, 
and  tertiary  feathers  are  geared  to  each  other  in  order  to 
rotate  in  one  direction  in  flexion,  and  in  another  and  opposite 
direction  in  extension,  is  shown  at  figs.  98,  99,  100,  and  101, 
p.  181.  In  flexion  the  feathers  open  up  and  permit  the  air 
to  pass  between  them.  In  extension  they  flap  together  and 
render  the  wing  as  air-tight  as  that  of  either  the  insect  or  bat. 
The  primary,  secondary,  and  tertiary  feathers  have  conse- 
quently a  valvular  action. 

The  Wing  of  the  Bird  not  always  opened  up  to  the  same  extent 
in  the  Up  Stroke. — The  elaborate  arrangements  and  adaptations 
for  increasing  the  area  of  the  wing,  and  making  it  impervious 
to  air  during  the  down  stroke,  and  for  decreasing  the  area 
and  opening  up  the  wing  during  the  up  stroke,  although 
necessary  to  the  flight  of  the  heavy-bodied,  short-winged 
birds,  as  the  grouse,  partridge,  and  pheasant,  are  by  no  means 
indispensable  to  the  flight  of  the  long-winged  oceanic  birds, 
unless  when  in  the  act  of  rising  from  a  level  surface ;  neither 
do  the  short-winged  heavy  birds  require  to  fold  and  open  up 
the  wing  during  the  up  stroke  to  the  same  extent  in  all  cases, 
less  folding  and  opening  up  being  required  when  the  birds 
fly  against  a  breeze,  and  when  they  have  got  fairly  under 
weigh.  All  the  oceanic  birds,  even  the  albatross,  require  to 
fold  and  flap  their  wings  vigorously  when  they  rise  from  the 
surface  of  the  water.  When,  however,  they  have  acquired  a 
certain  degree  of  momentum,  and  are  travelling  at  a  tolerable 
horizontal  speed,  they  can  in  a  great  measure  dispense  with 
the  opening  up  of  the  wing  during  the  up  stroke — nay,  more, 
they  can  in  many  instances  dispense  even  with  flapping. 
This  is  particularly  the  case  with  the  albatross,  which  (if  a 
tolerably  stiff  breeze  be  blowing)  can  sail  about  for  an  hour 
at  a  time  without  once  flapping  its  wings.  In  this  case  the 
wing  is  wielded  in  one  piece  like  the  insect  wing,  the  bird 
simply  screwing  and  unscrewing  the  pinion  on  and  off  the 
wind,  and  exercising  a  restraining  influence — the  breeze  doing 
the  principal  part  of  the  work.  In  the  bat  the  wing  is 
jointed  as  in  the  bird,  and  folded  during  the  up  stroke.  As, 


183 


however,  the  bat's  wing,  as  has  been  already  stated,  is  covered 
by  a  continuous  and  more  or  less  elastic  membrane,  it  follows 
that  it  cannot  be  opened  up  to  admit  of  the  air  passing 
through  it  during  the  up  stroke.  Flight  in  the  bat  is  therefore 
secured  by  alternately  diminishing  and  increasing  the  area  of 
the  wing  during  the  up  and  down  strokes — the  wing  rotating 
upon  its  root  and  along  its  anterior  margin,  and  presenting  a 
variety  of  kite-like  surfaces,  during  its  ascent  and  descent,  pre- 
cisely as  iu  the  bird  (fig.  80,  p.  149,  and  fig.  83,  p.  158). 


a 


FIG.  102. — Shows  the  upward  inclination  of  the  body  and  the  flexed  condition 
of  the  wings  (a  6,  ef;  a'  V,  e'f  )  in  the  flight  of  the  kingfisher.  The  body 
and  wings  when  taken  together  form  a  kite.  Compare  with  fly.  59,  p. 
126,  where  the  wings  are  fully  extended. 

Flexion  of  the  Wing  necessary  to  the  Flight  of  Birds. — Con- 
siderable diversity  of  opinion  exists  as  to  whether  birds  do  or 
do  not  flex  their  wings  in  flight.  The  discrepancy  is  owing 
to  the  great  difficulty  experienced  in  analysing  animal  move- 
ments, particularly  when,  as  in  the  case  of  the  wings,  they  are 
consecutive  and  rapid.  My  own  opinion  is,  that  the  wings 
are  flexed  in  flight,  but  that  all  wings  are  not  flexed  to  the 
same  extent,  and  that  what  holds  true  of  one  wing  does  not 
necessarily  hold  true  of  another.  To  see  the  flexing  of  the 
wing  properly,  the  observer  should  be  either  immediately 
above  the  bird  or  directly  beneath  it.  If  the  bird  be  con- 


184  ANIMAL  LOCOMOTION. 

templated  from  before,  behind,  or  from  the  side,  the  up  and 
down  strokes  of  the  pinion  distract  the  attention  and  compli- 
cate the  movement  to  such  an  extent  as  to  render  the  observa- 
tion of  little  value.  In  watching  rooks  proceeding  leisurely 
against  a  slight  breeze,  I  have  over  and  over  again  satisfied 
myself  that  the  Avings  are  flexed  during  the  up  stroke,  the 
mere  extension  and  flexion,  with  very  little  of  a  down  stroke, 
in  such  instances  sufficing  for  propulsion.  I  have  also  observed 
it  in  the  pigeon  in  full  flight,  and  likewise  in  the  starling, 
sparrow,  and  kingfisher  (fig.  102,  p.  183). 

It  occurs  principally  at  the  wrist-joint,  and  gives  to  the 
wing  the  peculiar  quiver  or  tremor  so  apparent  in  rapid 
flight,  and  in  young  birds  at  feeding-time.  The  object  to  be 
attained  is  manifest.  By  the  flexing  of  the  wing  in'  flight, 
the  "  remiges,"  or  rowing  feathers,  are  opened  up  or  thrown 
out  of  position,  and  the  air  permitted  to  escape — advantage 
being  thus  taken  of  the  peculiar  action  of  the  individual 
feathers  and  the  higher  degree  of  differentiation  perceptible  in 
the  wing  of  the  bird  as  compared  with  that  of  the  bat  and  insect. 

In  order  to  corroborate  the  above  opinion,  I  extended  the 
wings  of  several  birds  as  in  rapid  flight,  and  fixed  them  in 
the  outspread  position  by  lashing  them  to  light  unyielding 
reeds.  In  these  experiments  the  shoulder  and  elbow-joints 
were  left  quite  free — the  wrist  or  carpal  and  the  metacarpal 
joints  only  being  bound.  I  took  care,  moreover,  to  interfere 
as  little  as  possible  with  the  action  of  the  elastic  ligament  or 
alar  membrane  which,  in  ordinary  circumstances,  recovers  or 
flexes  the  wing,  the  reeds  being  attached  for  the  most  part  to 
the  primary  and  secondary  feathers.  When  the  wings  of  a 
pigeon  were  so  tied  up,  the  bird  could  not  rise,  although  it  made 
vigorous  efforts  to  do  so.  When  dropped  from  the  hand, 
it  fell  violently  upon  the  ground,  notwithstanding  the  strenu- 
ous exertions  which  it  made  with  its  pinions  to  save  itself. 
When  thrown  into  the  air,  it  fluttered  energetically  in  its 
endeavours  to  reach  the  dove  cot,  which  was  close  at  hand ; 
in  every  instance,  however,  it  fell,  more  or  less  heavily,  the 
distance  attained  varying  with  the  altitude  to  which  it  was 
projected. 

Thinking  that  probably  the  novelty  of  the  situation  and 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  185 

the  strangeness  of  the  appliances  confused  the  bird,  I  allowed 
it  to  walk  about  and  to  rest  without  removing  the  reeds.  I 
repeated  the  experiment  at  intervals,  but  with  no  better 
results.  The  same  phenomena,  I  may  remark,  were  witnessed  in 
the  sparrow ;  so  that  I  think  there  can  be  no  doubt  that  a  cer- 
tain degree  of  flexion  in  the  wings  is  indispensable  to  the  flight 
of  all  birds — the  amount  varying  according  to  the  length  and 
form  of  the  pinions,  and  being  greatest  in  the  short  broad- 
winged  birds,  as  the  partridge  and  kingfisher,  less  in  those 
whose  wings  are  moderately  long  and  narrow,  as  the  gulls,  and 
many  of  the  oceanic  birds,  and  least  in  the  heavy-bodied  long 
and  narrow- winged  sailing  or  gliding  birds,  the  best  example 
of  which  is  the  albatross.  The  degree  of  flexion,  moreover, 
varies  according  as  the  bird  is  rising,  falling,  or  progressing 
in  a  horizontal  direction,  it  being  greatest  in  the  two  former, 
and  least  in  the  latter. 

It  is  true  that  in  insects,  unless  perhaps  in  those  which 
fold  or  close  the  wing  during  repose,  no  flexion  of  the  pinion 
takes  place  in  flight ;  but  this  is  no  argument  against  this 
mode  of  diminishing  the  wing-area  during  the  up  stroke 
where  the  joints  exist ;  and  it  is  more  than  probable  that  when 
joints  are  present  they  are  added  to  augment  the  power  of 
the  wing  during  its  active  state,  i.e.  during  flight,  quite  as 
much  as  to  assist  in  arranging  the  pinion  on  the  back  or  side  of 
the  body  when  the  wing  is  passive  and  the  animal  is  reposing. 
The  flexion  of  the  wing  is  most  obvious  when  the  bird  is 
exerting  itself,  and  may  be  detected  in  birds  which  skim  or 
glide  when  they  are  rising,  or  when  they  are  vigorously  flap- 
ping their  wings  to  secure  the  impetus  necessary  to  the  gliding 
movement.  It  is  less  marked  at  the  elbow-joint  than  at  the 
wrist ;  and  it  may  be  stated  generally  that,  as  flexion  de- 
creases, the  twisting  flail-like  movement  of  the  wing  at  the 
shoulder  increases,  and  vice  versa, — the  great  difference  between 
sailing  birds  and  those  which  do  not  sail  amounting  to  this, 
that  in  the  sailing  birds  the  wing  is  worked  from  the  shoulder 
by  being  alternately  rolled  on  and  off  the  wind,  as  in  insects ; 
whereas,  in  birds  which  do  not  glide,  the  spiral  movement 
travels  along  the  arm  as  in  bats,  and  manifests  itself  during 
flexion  and  extension  in  the  bending  of  the  joints  and  in  the 


186  ANIMAL  LOCOMOTION.. 

rotation  of  the  bones  of  the  wing  on  their  axes.  The  spiral 
conformation  of  the  pinions,  to  which  allusion  has  been  so 
frequently  made,  is  best  seen  in  the  heavy -bodied  birds,  as  the 
turkey,  capercailzie,  pheasant,  and  partridge;  and  here  also 
the  concavo-convex  form  of  the  wing  is  most  perceptible.  In. 
the  light-bodied,  ample-winged  birds,  the  amount  of  twisting 
is  diminished,  and,  as  a  result,  the  wing  is  more  or  less  flat- 
tened, as  in  the  sea-gull  (fig.  103). 


Fio.  103. — Shows  the  twisted  levers  or  screws  formed  by  the  wings  of  the  gulL 
Compare  with  fig.  53,  p.  107  ;  with  figs.  76,  77,  and  78,  p.  147,  and  with  ligs. 
82  and  83,  p.  158.— Original. 

Consideration  of  the  Forces  which  propel  the  Wings  of  Insects. 
• — In  the  thorax  of  insects  the.  muscles  are  arranged  in  two 
principal  sets  in  the  form  of  a  cross — i.e.  there  is  a  powerful 
vertical  set  which  runs  from  above  downwards,  and  a  powerful 
antero-posterior  set  which  runs  from  before  backwards.  There 
are  likewise  a  few  slender  muscles  which  proceed  in  a  more 
or  less  oblique  direction.  The  antero-posterior  and  vertical 
sets  of  muscles  are  quite  distinct,  as  are  likewise  the  oblique 
muscles.  Portions,  however,  of  the  vertical  and  oblique 
muscles  terminate  at  the  root  of  the  wing  in  jelly-looking 
points  which  greatly  resemble  rudimentary  tendons,  so  that  I 
am  inclined  to  believe  that  the  vertical  and  oblique  muscles 
exercise  a  direct  influence  on  the  movements  of  the  wing. 
The  shortening  of  the  antero-posterior  set  of  muscles  (indi- 
rectly assisted  by  the  oblique  ones)  elevates  the  dorsum  of  the 
thorax  by  causing  its  anterior  extremity  to  approach  its 
posterior  extremity,  and  by  causing  the  thorax  to  bulge  out 
or  expand  laterally.  This  change  in  the  thorax  necessitates 
the  descent  of  the  wing.  The  shortening  of  the  vertical  set 
(aided  by  the  oblique  ones)  has  a  precisely  opposite  effect, 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  187 

and  necessitates  its  ascent.  While  the  wing  is  ascending  and 
descending  the  oblique  muscles  cause  it  to  rotate  on  its  long 
axis,  the  bipartite  division  of  the  wing  at  its  root,  the  spiral 
configuration  of  the  joint,  and  the  arrangement  of  the  elastic 
and  other  structures  which  connect  the  pinion  with  the  body, 
together  with  the  resistance  it  experiences  from  the  air,  con- 
ferring on  it  the  various  angles  which  characterize  the  down 
and  up  strokes.  The  wing  may  therefore  be  said  to  be  de- 
pressed by  the  shortening  of  the  antero-posterior  set  of 
muscles,  aided  by  the  oblique  muscles,  and  elevated  by  the 
shortening  of  the  vertical  and  oblique  muscles,  aided  by  the 
elastic  ligaments,  and  the  reaction  of  the  air.  If  we  adopt 
this  view  we  have  a  perfect  physiological  explanation  of  the 
phenomenon,  as  we  have  a  complete  circle  or  cycle  of  motion, 
the  antero-posterior  set  of  muscles  shortening  when  the 
vertical  set  of  muscles  are  elongating,  and  vice  versA.  This,  I 
may  add,  is  in  conformity  with  all  other  muscular  arrange- 
ments, where  we  have  what  are  usually  denominated  exten- 
sors and  flexors,  pronators  and  supinators,  abductors  and 
adductors,  etc.,  but  which,  as  I  have  already  explained  (pp. 
24  to  34),  are  simply  the  two  halves  of  a  circle  of  muscle  and 
of  motion,  an  arrangement  for  securing  diametrically  opposite 
movements  in  the  travelling  .surfaces  of  all  animals. 

Chabrier's  account,  which  I  subjoin,  virtually  supports  this 
hypothesis : — 

"  It  is  generally  through  the  intervention  of  the  proper 
motions  of  the  dorsum,  which  are  very  considerable  during 
flight,  that  the  wings  or  the  elytra  are  moved  equally  and 
simultaneously.  Thus,  when  it  is  elevated,  it  carries  with  it 
the  internal  side  of  the  base  of  the  wings  with  which  it  is 
articulated,  from  which  ensues  the  depression  of  the  external 
side  of  the  wing ;  and  when  it  approaches  the  sternal  portion 
of  the  trunk,  the  contrary  takes  place.  During  the  depres- 
sion of  the  wings,  the  dorsum  is  curved  from  before  back- 
wards, or  in  such  a  manner  that  its  anterior  extremity  is 
brought  nearer  to  its  posterior,  that  its  middle  is  elevated, 
and  its  lateral  portions  removed  further  from  each  other. 
The  reverse  takes  place  in  the  elevation  of  the  wings ;  the 
anterior  extremity  of  the  dorsum  being  removed  to  a  greater 


188  ANIMAL  LOCOMOTION. 

distance  from  the  posterior,  its  middle  being  depressed,  and 
its  sides  brought  nearer  to  each  other.  Thus  its  bending  in 
one  direction  produces  a  diminution  of  its  curve  in  the  direc- 
tion normally  opposed  to  it ;  and  by  the  alternations  of  this 
motion,  assisted  by  other  means,  the  body  is  alternately  com- 
pressed and  dilated,  and  the  wings  are  raised  and  depressed 
by  turns."1 

In  the  libellulcB  or  dragon-flies,  the  muscles  are  inserted 
into  the  roots  of  the  wings  as  in  the  bat  and  bird,  the  only 
difference  being  that  in  the  latter  the  muscles  creep  along  the 
wings  to  their  extremities. 

In  all  the  wings  which  I  have  examined,  whether  in  the 
insect,  bat,  or  bird,  the  wings  are  recovered,  flexed,  or 
drawn  towards  the  body  by  the  action  of  elastic  ligaments, 
these  structures,  by  their  mere  contraction,  causing  the 
wings,  when  fully  extended  and  presenting  their  maximum 
of  surface,  to  resume  their  position  of  rest,  and  plane  of 
least  resistance.  The  principal  effort  required  in  flight 
would  therefore  seem  to  be  made  during  extension  and 
the  down  stroke.  The  elastic  ligaments  are  variously  formed, 
and  the  amount  of  contraction  which  they  undergo  is  in 
all  cases  accurately  adapted  to  the  size  and  form  of  the 
wings,  and  the  rapidity  with  which  they  are  worked — the 
contraction  being  greatest  in  the  short-winged  and  heavy- 
bodied  insects  and  birds,  and  least  in  the  light-bodied  and 
ample-winged  ones,  particularly  in  such  as  skim  or  glide. 
The  mechanical  action  of  the  elastic  ligaments,  I  need  scarcely 
remark,  insures  a  certain  period  of  repose  to  the  wings 
at  each  stroke,  and  this  is  a  point  of  some  importance,  as 
showing  that  the  lengthened  and  laborious  flights  of  insects 
and  birds  are  not  without  their  stated  intervals  of  rest. 

Speed  attained  by  Insects. — Many  instances  might  be  quoted 
of  the  marvellous  powers  of  flight  possessed  by  insects  as  a 
class.  The  male,  of  the  silkworm-moth  (Attacus  Paphia)  is 
stated  to  travel  more  than  100  miles  a  day;2  and  an  anony- 
mous writer  in  Nicholson's  Journal3  calculates  that  the  com- 
mon house-fly  (Musca  domeslica),  in  ordinary  flight,  makes  600 

1  Chabrier,  as  rendered  by  E.  F.  Bennett,  F.L.S.,  etc. 

a  Linn.  Trans,  vii.  p.  40.  3  Vol.  iii.  p.  36. 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  189 

strokes  per  second,  and  advances  twenty-five  feet,  but  that 
the  rate  of  speed,  if  the  insect  be  alarmed,  may  be  increased 
six  or  seven  fold,  so  that  under  certain  circumstances  it  can 
outstrip  the  fleetest  racehorse.  Every  one  when  riding  on  a 
warm  summer  day  must  have  been  struck  with  the  cloud  of 
flies  which  buzz  about  his  horse's  ears  even  when  the  animal 
is  urged  to  its  fastest  paces ;  and  it  is  no  uncommon  thing 
to  see  a  bee  or  a  wasp  endeavouring  to  get  in  at  the  window 
of  a  railway  car  in  full  motion.  If  a  small  insect  like  a  fly 
can  outstrip  a  racehorse,  an  insect  as  large  as  a  horse  would 
travel  very  much  faster  than  a  cannon-ball.  Leeuwenhoek 
relates  a  most  exciting  chase  which  he  once  beheld  in  a 
menagerie  about  100  feet  long  between  a  swallow  and  a 
dragon-fly  (Mordella).  The  insect  flew  with  incredible  speed, 
and  wheeled  with  such  address,  that  the  swallow,  notwith- 
standing its  utmost  efforts,  completely  failed  to  overtake  and 
capture  it.1 

Consideration  of  the  Forces  which  propel  the  Wings  of  Bats 
and  Birds. — The  muscular  system  of  birds  has  been  so  fre- 
quently and  faithfully  described,  that  I  need  not  refer  to  it 
further  than  to  say  that  there  are  muscles  which  by  their 
action  are  capable  of  elevating  and  depressing  the  wings,  and 
of  causing  them  to  move  in  a  forward  and  backward  direction, 
and  obliquely.  They  can  also  extend  or  straighten  and 
bend,  or  flex  the  wings,  and  cause  them  to  rotate  in  the 
direction  of  their  length  during  the  down  and  up  strokes. 
The  muscles  principally  concerned  in  the  elevation  of  the 
wings  are  the  smaller  pectoral  or  breast  muscles  (pedorales 
minor) ;  those  chiefly  engaged  in  depressing  the  wings  are  the 
larger  pectorals  (pedorales  major).  The  pectoral  muscles  cor- 
respond to  the  fleshy  mass  found  on  the  breast-bone  or 
sternum,  which  in  flying  birds  is  boat-shaped,  and  furnished 
with  a  keel.  These  muscles  are  sometimes  so  powerful  and 
heavy  that  they  outweigh  all  the  other  muscles  of  the  body. 

1  "  The  hobby  falcon,  which  abounds  in  Bulgaria  during  the  summer 
months,  hawks  large  dragon/lies,  which  it  seizes  with  the  foot  and  devours 
whilst  in  the  air.  It  also  kills  swifts,  larks,  turtle-doves,  and  bee-birds,  al- 
though more  rarely." — Falconry  in  the  British  Isles,  by  Francis  Henry  Salvin 
and  William  Brcirick.  Lond,  1855. 


1 90  ANIMAL  LOCOMOTION. 

The  power  of  the  bird  is  thus  concentrated  for  the  purpose  of 
moving  the  wings  and  conferring  steadiness  upon  the  volant 
mass.  In  birds  of  strong  flight  the  keel  is  very  large,  in 
order  to  afford  ample  attachments  for  the  muscles  delegated  to 
move  the  wings.  In  birds  which  cannot  fly,  as  the  members 
of  the  ostrich  family,  the  breast-bone  or  sternum  has  no  keel.1 

The  remarks  made  regarding  the  muscles  of  birds,  apply 
with  very  slight  modifications  to  the  muscles  of  bats.  The 
muscles  of  bats  and  birds,  particularly  those  of  the  wings, 
are  geared  to,  and  act  in  concert  with,  elastic  ligaments  or 
membranes,  to  be  described  presently. 

Lax  condition  of  the  Shoulder-Joint  in  Bats,  Birds,  etc. — The 
great  laxity  of  the  shoulder-joint  in  bats  and  birds,  readily 
admits  of  their  bodies  falling  downwards  and  forwards  during 
the  up  stroke.  This  joint,  as  has  been  already  stated,  admits 
of  movement  in  every  direction,  so  that  the  body  of  the  bat 
or  bird  is  like  a  compass  set  upon  gimbals,  i.e.  it  swings  and 
oscillates,  and  is  equally  balanced,  whatever  the  position  of 
the  wings.  The  movements  of  the  shoulder-joint  in  the  bird, 
bat,  and  insect  are  restrained  within  certain  limits  by  a 
system  of  check  ligaments  and  prominences ;  but  in  each 
case  the  range  of  motion  is  very  great,  the  wings  being  per- 
mitted to  swing  forwards,  backwards,  upwards,  downwards, 
or  at  any  degree  of  obliquity.  They  are  also  permitted  to 
rotate  along  their  anterior  margin,  or  to  twist  in  the  direction 
of  their  length  to  the  extent  of  nearly  a  quarter  of  a  turn. 
This  great  freedom  of  movement  at  the  shoulder-joint  enables 
the  insect,  bat,  and  bird  to  rotate  and  balance  upon  two 
centres — the  one  running  in  the  direction  of  the  length  of  the 
body,  the  other  at  right  angles  or  across  the  body,  i.e.  in 
the  direction  of  the  length  of  the  wings. 

In  the  bird  the  head  of  the  humerus  is  convex  and  some- 
what oval  (not  round),  the  long  axis  of  the  oval  being  directed 
from  above  downwards,  i.e.  from  the  dorsal  towards  the  ven- 
tral aspect  of  the  bird.  The  humerus  can,  therefore,  glide  up 
and  down  in  the  facettes  occurring  on  the  articular  ends  of  the 

1  One  of  the  best  descriptions  of  the  bones  and  muscles  of  the  bird  is  that 
given  by  Mr.  Macgillivray  in  his  very  admirable,  voluminous,  and  entertain- 
ing work,  entitled  History  of  British  Birds.  Lond.  1837. 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  191 

coracoid  and  scapular  bones  with  great  facility,  much  in  the 
same  way  that  the  head  of  the  radius  glides  upon  the  distal 
end  of  the  humerus.  But  the  humerus  has  another  motion  ; 
it  moves  like  a  hinge  from  before  backwards,  and  vice  versa. 
The  axis  of  the  latter  movement  is  almost  at  right  angles  to 
that  of  the  former.  As,  however,  the  shoulder-joint  is  con- 
nected by  long  ligaments  to  the  body,  and  can  be  drawn 
away  from  it  to  the  extent  of  one-eighth  of  an  inch  or  more, 
it  follows  that  a  third  and  twisting  movement  can  be  performed, 
the  twisting  admitting  of  rotation  to  the  extent  of  something 
like  a  quarter  of  a  turn.  In  raising  and  extending  the  wing 
preparatory  to  the  downward  stroke  two  opposite  movements 
are  required,  viz.  one  from  before  backwards,  and  another 
from  below  upwards.  As,  however,  the  axes  of  these  move- 
ments are  at  nearly  right  angles  to  each  other,  a  spiral  or 
twisting  movement  is  necessary  to  run  the  one  into  the 
other — to  turn  the  corner,  in  fact. 

From  what  has  been  stated  it  will  be  evident  that  the 
movements  of  the  wing,  particularly  at  the  root,  are  remark- 
ably free,  and  very  varied.  A  directing  and  restraining,  as 
well  as  a  propelling  force,  is  therefore  necessary. 

The  guiding  force  is  to  be  found  in  the  voluntary  muscles 
which  connect  the  wing  with  the  body  in  the  insect,  and 
which  in  the  bat  and  bird,  in  addition  to  connecting  the 
wing  with  the  body,  extend  along  the  pinion  even  to  its  tip. 
It  is  also  to  be  found  in  the  musculo-elastic  and  other  liga- 
ments, seen  to  advantage  in  the  bird. 

The  Wing  flexed  and  partly  elevated  by  the  Action  of  Elastic 
Ligaments — the  Nature  and  Position  of  such  Ligaments  in  the 
Pheasant,  Snipe,  Crested  Crane,  Swan,  etc. — When  the  wing  is 
drawn  away  from  the  body  of  the  bird  by  the  hand  the 
posterior  margin  of  the  pinion  formed  by  the  primary, 
secondary,  and  tertiary  feathers  rolls  down  to  make  a  variety 
of  inclined  surfaces  with  the  horizon  (cb,  of  fig.  63,  p.  138). 
When,  however,  the  hand  is  withdrawn,  even  in  the  dead 
bird,  the  wing  instantly  folds  up ;  and  in  doing  so  reduces 
the  amount  of  inclination  in  the  several  surfaces  referred 
to  (cb,def  of  the  same  figure).  The  wing  is  folded  by 
the  action  of  certain  elastic  ligaments,  which  are  put  upon 


192  ANIMAL  LOCOMOTION. 

the  stretch  in  extension,  and  which  recover  their  original  form 
and  position  in  flexion  (fig.  98,  c,  p.  181).  This  simple  ex- 
periment shows  that  the  various  inclined  surfaces  requisite 
for  flight  are  produced  by  the  mere  acts  of  extension  and 
Hexion  in  the  dead  bird.  It  is  not,  however,  to  be  inferred 
from  this  circumstance  that  flight  can  be  produced  without 
voluntary  movements  any  more  than  ordinary  walking.  The 
muscles,  bones,  ligaments,  feathers,  etc.,  are  so  adjusted  with 
reference  to  each  other  that  if  the  wing  is  moved  at  all, 
it  must  move  in  the  proper  direction — an  arrangement  which 
enables  the  bird  to  fly  without  thinking,  just  as  we  can 
walk  without  thinking.  There  cannot,  however,  be  a  doubt 
that  the  bird  has  the  power  of  controlling  its  wings  both 
during  the  down  and  up  strokes ;  for  how  otherwise  could 
it  steer  and  direct  its  course  with  such  precision  in  obtain- 
ing its  food  1  how  fix  its  wings  on  a  level  with  or  above 
its  body  for  skimming  purposes  1  how  fly  in  a  curve  1  how 
fly  with,  against,  or  across  a  breeze  1  how  project  itself  from 
a  rock  directly  into  space,  or  how  elevate  itself  from  a  level 
surface  by  the  laboured  action  of  its  wings  1 

The  wing  of  the  bird  is  elevated  to  a  certain  extent  in 
flight  by  the  reaction  of  the  air  upon  its  under  surface  ;  but 
it  is  also  elevated  by  muscular  action — by  the  contraction  of 
the  elastic  ligaments,  and  by  the  body  falling  downwards  and 
forwards  in  a  curve. 

That  muscular  action  is  necessary  is  proved  by  the  fact 
that  the  pinion  is  supplied  with  distinct  elevator  muscles.1 
It  is  further  proved  by  this,  that  the  bird  can,  and  always 
1  Mr.  Macgillivray  and  C.  J.  L.  Krarup,  a  Danish  author,  state  that  the 
wing  is  elevated  by  a  vital  force,  viz.  by  the  contraction  of  the  pectoralis 
miiior.  This  muscle,  according  to  Krarup,  acts  with  one-eighth  the  intensity 
of  the  pectoralis  major  (the  depressor  of  the  wjpg).  He  bases  his  statement 
upon  the  fact  that  in  the  pigeon  the  pectoralis  minor  or  elevator  of  the  wing 
weighs  one-eighth  of  an  ounce,  whereas  the  pectoralis  major  or  depressor  of 
the  wing  weighs  seven-eighths  of  an  ounce.  It  ought,  however,  to  be  borne  in 
mind  that  the  volume  of  a  muscle  does  not  necessarily  determine  the  precise 
influence  exerted  by  its  action  ;  for  the  tendon  of  the  muscle  may  be  made  to 
act  upon  a  long  lever,  and,  under  favourable  conditions,  for  developing  its 
powers,  while  that  of  another  muscle  may  be  made  to  act  upon  a  short  lever, 
and,  consequently,  under  unfavourable  conditions. — On  the  Flight  of  Birds, 
p.  30.  Copenhagen,  1869. 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  193 

does,  elevate  its  wings  prior  to  flight,  quite  independently  of 
the  air.  When  the  bird  is  fairly  launched  in  space  the 
elevator  muscles  are  assisted  by  the  tendency  which  the  body 
has  to  fall  downwards  and  forwards  :  by  the  reaction  of  the 
air;  and  by  the  contraction  of  the  elastic  ligaments.  The 
air  and  the  elastic  ligaments  contribute  to  the  elevation  of 
the  wing,  but  both  are  obviously  under  control — they,  in  fact, 
form  links  in  a  chain  of  motion  which  at  once  begins  and 
terminates  in  the  muscular  system. 

That  the  elastic  ligaments  are  subsidiary  and  to  a  certain 
extent  under  the  control  of  the  muscular  system  in  the  same 
sense  that  the  air  is,  is  evident  from  the  fact  that  voluntary 
muscular  fibres  run  into  the  ligaments  in  question  at  various 
points  (a,  b  of  fig.  98,  p.  181).  The  ligaments  and  muscular 
fibres  act  in  conjunction,  and  fold  or  flex  the  forearm  on  the 
arm.  There  are  others  which  flex  the  hand  upon  the  forearm. 
Others  draw  the  wing  towards  the  body. 

The  elastic  ligaments,  while  occupying  a  similar  position  in 
the  wings  of  all  birds,  are  variously  constructed  and  variously 
combined  with  voluntary  muscles  in  the  several  species. 

The  Elastic  Ligaments  more  highly  differentiated  in  Wings 
which  vibrate  rapidly. — The  elastic  ligaments  of  the  swan  are 
more  complicated  and  more  liberally  supplied  with  voluntary 
muscle  than  those  of  the  crane,  and  this  is  no  doubt  owing  to 
the  fact  that  the  wings  of  the  swan  are  driven  at  a  much 
higher  speed  than  those  of  the  crane.  In  the  snipe  the  wings 
are  made  to  vibrate  very  much  more  rapidly  than  in  the  swan, 
and,  as  a  consequence,  we  find  that  the  fibro-elastic  bands  are 
not  only  greatly  increased,  but  they  are  also  geared  to  a  much 
greater  number  of  voluntary  muscles,  all  which  seems  to 
prove  that  the  musculo-elastic  apparatus  employed  for  recover- 
ing or  flexing  the  wing  towards  the  end  of  the  down  stroke, 
becomes  more  and  more  highly  differentiated  in  proportion  to 
the  rapidity  with  which  the  wing  is  moved.1  The  reason  for 
this  is  obvious.  If  the  wing  is  to  be  worked  at  a  higher 
speed,  it  must,  as  a  consequence,  be  more  rapidly  flexed  and 

1  A  careful  account  of  the  musculo-elastic  structures  occurring  in  the  wing 
of  the  pigeon  is  given  by  Mr.  Macgillivray  in  bis  History  jf  British  Birds, 
pp.  37,  38. 


194  ANIMAL  LOCOMOTION. 

extended.  The  rapidity  with  which  the  wing  of  the  bird  is 
extended  and  flexed  is  in  some  instances  exceedingly  great ; 
so  great,  in  fact,  that  it  escapes  the  eye  of  the  ordinary  observer. 
The  speed  with  which  the  wing  darts  in  and  out  in  flexion 
and  extension  would  be  quite  inexplicable,  but  for  a  know- 
ledge of  the  fact  that  the  different  portions  of  the  pinion  form 
angles  with  each  other,  these  angles  being  instantly  increased 
or  diminished  by  the  slightest  quiver  of  the  muscular  and 
fibre-elastic  systems.  If  we  take  into  account  the  fact  that 
the  wing  of  the  bird  is  recovered  or  flexed  by  the  combined 
action  of  voluntary  muscles  and  elastic  ligaments ;  that  it  is 
elevated  to  a  considerable  extent  by  voluntary  muscular  effort ; 
and  that  it  is  extended  and  depressed  entirely  by  muscular 
exertion,  we  shall  have  difficulty  in  avoiding  the  conclusion 
that  the  wing  is  thoroughly  under  the  control  of  the  muscular 
system,  not  only  in  flexion  and  extension,  but  also  throughout 
the  entire  down  and  up  strokes. 

An  arrangement  in  every  respect  analogous  to  that  described 
in  the  b*ird  is  found  in  the  wing  of  the  bat,  the  covering  or 
web  of  the  wing  in  this  instance  forming  the  principal  elastic 
ligament  (fig.  17,  p.  36). 

Power  of  the  Wing — to  what  owing. — The  shape  and  power 
of  the  pinion  depend  upon  one  of  three  circumstances — to 
wit,  the  length  of  the  humerus,1  the  length  of  the  cubitus  or 
forearm,  and  the  length  of  the  primary  feathers.  In  the 
swallow  the  humerus,  and  in  the  humming-bird  the  cubitus, 
is  very  short,  the  primaries  being  very  long ;  whereas  in  the 
albatross  the  humerus  or  arm-bone  is  long  and  the  primaries 
short.  When  one  of  these  conditions  is  fulfilled,  the  pinion 
is  usually  greatly  elongated  and  scythe-like  (fig.  62,  p.  137) 
— an  arrangement  which  enables  the  bird  to  keep  on  the 
wing  for  immense  periods  with  comparatively  little  exertion, 
and  to  wheel,  turn,  and  glide  about  with  exceeding  ease  and 
grace.  When  the  wing  is  truncated  and  rounded  (fig.  96,  p. 

1  "The  humerus  varies  extremely  in  length,  being  very  short  in  the  swal- 
low, of  moderate  length  in  the  gallinaceous  birds,  longer  in  the  crows,  very 
long  in  the  ganuets,  and  unusually  elongated  in  the  albatross.  In  the  golden 
eagle  it  is  also  seen  to  be  of  great  length." — Macgillivray's  British  Birds, 
vol.  i.  p.  30. 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  195 

176),  a  form  of  pinion  usually  associated  with  a  heavy  body, 
as  in  the  grouse,  quail,  diver,  and  grebe,  the  muscular  exer- 
tion required,  and  the  rapidity  with  which  the  wing  moves 
are  very  great;  those  birds,  from  a  want  of  facility  in  turning, 
flying  either  in  a  straight  line  or  making  large  curves.  They, 
moreover,  rise  with  difficulty,  and  alight  clumsily  and  some- 
what suddenly.  Their  flight,  however,  is  perfect  while  it  lasts. 

The  goose,  duck  (fig.  107,  p.  204),  pigeon  (fig.  106,  p. 
203)  and  crow,  are  intermediate  both  as  regards  the  form 
of  the  wing  and  the  rapidity  with  which  it  is  moved. 

The  heron  (fig.  60,  p.  126)  and  humming-bird  furnish  ex- 
treme examples  in  another  direction, — the  heron  having  a 
large  wing  with  a  leisurely  movement,  the  humming-bird  a 
comparatively  large  wing  with  a  greatly  accelerated  one. 

But  I  need  not  multiply  examples ;  suffice  it  to  say  that 
flight  may  be  attained  within  certain  limits  by  every  size  and 
form  of  wing,  if  the  number  of  its  oscillations  be  increased  in 
proportion  to  the  weight  to  be  raised. 

Reasons  why  the  effective  Stroke  should  be  delivered  downwards 
and  forwards. — The  wings  of  all  birds,  whatever  their  form, 
act  by  alternately  presenting  oblique  and  comparatively  non- 
oblique  surfaces  to  the  air, — the  mere  extension  of  the  pinion, 
as  has  been  shown,  causing  the  primary,  secondary,  and  ter- 
tiary feathers  to  roll  down  till  they  make  an  angle  of  30°  or 
so  with  the  horizon,  in  order  to  prepare  it  for  giving  the 
effective  stroke,  which  is  delivered,  with  great  rapidity  and 
energy,  in  a  downward  and  forward  direction.  I  repeat, 
"  downwards  and  forwards ; "  for  a  careful  examination  of 
the  relations  of  the  wing  in  the  dead  bird,  and  a  close  ob- 
servation of  its  action  in  the  living  one,  supplemented  by  a 
large  number  of  experiments  with  natural  and  artificial 
wings,  have  fully  convinced  me  that  the  stroke  is  invariably 
delivered  in  this  direction.1  If  the  wing  did  not  strike 

1  Prevailing  Opinions  as  to  the  Direction  of  the  Down  Stroke. — Mr.  Macgil- 
livray,  in  his  History  of  British  Birds,  published  in  1837,  states  (p.  34) 
that  in  flexion  the  wing  is  drawn  upwards,  forwards,  and  inwards,  but 
that  during  extension,  when  the  effective  stroke  is  given,  it  is  made  to 
strike  outwards,  downwards,  and  backwards.  The  Duke  of  Argyll  holds 
a  similar  opinion.  In  speaking  of  the  hovering  of  birds,  he  asserts  that, 


196  ANIMAL  LOCOMOTION. 

downwards  and  forwards,  it  would  act  at  a  manifest  dis- 
advantage : — 

1st.  Because  it  would  present  the  back  or  convex  surface  of 
the  wing  to  the  air — a  convex  surface  dispersing  or  dissipating 
the  air,  while  a  concave  surface  gathers  it  together  or  focuses  it. 

2d.  In  order  to  strike  backwards  effectually,  the  concavity 
of  the  wing  would  also  require  to  be  turned  backwards ;  and 
this  would  involve  the  depression  of  the  anterior  or  thick 
margin  of  the  pinion,  and  the  elevation  of  the  posterior  or 
thin  one,  during  the  down  stroke,  which  never  happens. 

3d.  The  strain  to  which  the  pinion  is  subjected  in  flight 
would,  if  the  wing  struck  backwards,  fall,  not  on  the  anterior 
or  strong  margin  of  the  pinion  formed  by  the  bones  and 
muscles,  but  on  the  posterior  or  weak  margin  formed  by  the 
tips  of  the  primary,  secondary,  and  tertiary  feathers — which 
is  not  in  accordance  with  the  structure  of  the  parts. 

4  th.  The  feathers  of  the  wing,  instead  of  being  closed,  as 
they  necessarily  are,  by  a  downward  and  forward  movement, 

"  if  a  bird,  by  altering  the  axis  of  its  own  body,  can  direct  its  wing  stroke 
in  some  degree  forwards,  it  will  have  the  effect  of  stopping  instead  of 
promoting  progression ; "  and  that,  "  Except  for  the  purpose  of  arresting 
their  flight,  birds  can  never  strike  except  directly  downwards — that  is, 
directly  against  the  opposing  force  of  gravity."— Good  Words,  Feb.  1865, 
p.  132. 

Mr.  Bishop,  in  the  Cyc.  of  Anat.  and  Phys.,  vol.  iii.  p.  425,  says,  "In 
consequence  of  the  planes  of  the  wings  being  disposed  either  perpendicularly 
or  obliquely  backwards  to  the  direction  of  their  motion,  a  corresponding  im- 
pulse is  given  to  their  centre  of  gravity."  Professor  Owen,  in  like  manner, 
avers  that  "  a  downward  stroke  would  only  tend  to  raise  the  bird  in  the  air ; 
to  carry  it  forwards,  the  wings  require  to  be  moved  in  an  oblique  plane,  so 
as  to  strike  backwards  as  well  as  downwards."— Comp.  Anat.  and  Phys.  and 
Vertebrates,  vol.  ii.  p.  115. 

The  following  is  the  account  given  by  M.  E.  Liais  :— "  When  a  bird  is  about 
to  depress  its  wing,  this  is  a  little  inclined  from  before  backwards.  When 
the  descending  movement  commences,  the  wing  does  not  descend  parallel  to 
itself  in  a  direction  from  before  backwards  ;  but  the  movement  is  accompanied 
by  a  rotation  of  several  degrees  round  the  anterior  edge,  so  that  the  wing 
becomes  more  in  front  than  behind,  and  the  descending  movement  is  trans- 
ferred more  and  more  backwards.  .  .  .  When  the  wing  has  completely 
descended,  it  is  both  further  back  and  lower  than  at  the  commencement  of 
the  movement."— "  On  the  Flight  of  Birds  and  Insects."  Annals  of  Nat. 
Hist.  vol.  xv.  3d  series,  p.  156. 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  197 

would  be  inevitably  opened,  and  the  integrity  of  the  wing 
impaired  by  a  downward  and  backward  movement. 

5th.  The  disposition  of  the  articular  surfaces  of  the  wing 
(particularly  that  of  the  shoulder-joint)  is  such  as  to  facilitate 
the  downward  and  forward  movement,  while  it  in  a  great 
measure  prevents  the  downward  and  backward  one. 

6/A  and  lastly.  If  the  wing  did  in  reality  strike  downwards 
and  backwards,  a  result  the  converse  of  that  desired  would 
most  assuredly  be  produced,  as  an  oblique  surface  which 
smites  the  air  in  a  downward  and  backward  direction  (if 
left  to  itself)  tends  to  depress  the  body  bearing  it.  This  is 
proved  by  the  action  upon  the  air  of  fr,ee  inclined  planes, 
arranged  in  the  form  of  a  screw. 

The  Wing  acts  as  an  Elevator,  Propeller,  and  Sustainer,  both 
during  extension  and  flexion. — The  wing,  as  has  been  ex- 
plained, is  recovered  or  drawn  off  the  wind  principally  by  the 
contraction  of  the  elastic  ligaments  extending  between  the 
joints,  so  that  the  pinion  during  flexion  enjoys  a  certain 
degree  of  repose.  The  time  occupied  in  recovering  is  not 
lost  so  long  as  the  wing  makes  an  angle  with  the  horizon 
and  the  bird  is  in  motion,  it  being  a  matter  of  indifference 
whether  the  wing  acts  on  the  air,  or  the  air  on  the  wing,  so 
long  as  the  body  bearing  the  latter  is  under  weigh ;  and  this 
is  the  chief  reason  why  the  albatross,  which  is  a  very  heavy 
bird,1  can  sail  about  for  such  incredible  periods  without  flap- 
ping the  wings  at  all.  Captain  Hutton  thus  graphically 
describes  the  sailing  of  this  magnificent  bird  : — "  The  flight  of 
the  albatross  is  truly  majestic,  as  with  outstretched  motionless 
wings  he  sails  over  the  surface  of  the  sea — now  rising  high 
in  air,  now  with  a  bold  sweep,  and  wings  inclined  at  an  angle 
with  the  horizon,  descending  until  the  tip  of  the  lower  one  all 
but  touches  the  crest  of  the  waves  as  he  skims  over  them."2 

Birds  of  Flight  divisible  into  four  kinds : — 

1st.  Such  as  have  heavy  bodies  and  short  wings  with  a 
rapid  movement  (fig.  59,  p.  126). 

1  The  average  weight  of  the  albatross,  as  given  by  Gould,  is  171bs. — Ibis, 
2d  series,  vol.  i.  1865,  p.  295. 

8  "  On  some  of  the  Birds  inhabiting  the  Southern  Ocean,"  by  Capt.  F.  W. 
Button.— Ibis,  2d  series,  vol.  i.  1865,  p.  282. 


198  ANIMAL  LOCOMOTION. 

2d.  Such  as  have  light  bodies  and  large  wings  with  a 
leisurely  movement  (fig.  60,  p.  126;  fig.  103,  p.  186). 

3d.  Such  as  have  heavy  bodies  and  long  narrow  wings 
with  a  decidedly  slow  movement  (fig.  105,  p.  200). 

4th.  Such  as  are  intermediate  with  regard  to  the  size  of 
body,  the  dimensions  of  the  wing,  and  the  energy  with  which 
it  is  driven  (fig.  102,  p.  183;  fig.  106,  p.  203;  fig.  107, 
p.  204). 

They  may  be  subdivided  into  those  which  float,  skim,  or 
glide,  and  those  which  fly  in  a  straight  line  and  irregularly. 

The  pheasant,  partridge  (fig.  59,  p.  126),  grouse,  and  quail, 
furnish  good  examples  of  the  heavy-bodied,  short-winged 
birds.  In  these  the  wing  is  rounded  and  deeply  concave. 
It  is,  moreover,  wielded  with  immense  velocity  and  power. 

The  heron  (fig.  60,  p.  126),  sea-mew  (fig.  103,  p.  186),  lap- 
wing (fig.  63,  p.  138),  and  owl  (fig.  104),  supply  examples  of 
the  second  class,  where  the  wing,  as  compared  with  the  body, 
is  very  ample,  and  where  consequently  it  is  moved  more 
leisurely  and  less  energetically. 


FIG.  104.— The  Cape  Barn-Owl  (Strix  capensis,  Smith),  as  seen  in  full  flight, 
hunting.  The  under  surface  of  the  wings  and  body  are  inclined  slightly 
upwards,  and  act  upon  the  air  after  the  manner  of  a  kite.  (Compare  with 
fig.  59,  p.  126,  aud  fig.  102,  p.  183.)— Original. 

The  albatross  (fig.  105,  p.  200)  and  pelican  afford  in- 
stances of  the  third  class,  embracing  the  heavy-bodied,  long- 
winged  birds. 

The  duck  (fig.  107,  p.  204),  pigeon  (fig.  106,  p.  203),  crow 
and  thrush,  are  intermediate,  both  as  regards  the  size  of  the 
wing  and  the  rapidity  with  which  it  is  made  to  oscillate. 
These  constitute  the  fourth  class. 

The  albatross  (fig.  105,  p.  200),  swallow,  eagle,  and  hawk, 
provide  instances  of  sailing  or  gliding  birds,  where  the  wing 
is  ample,  elongated,  and  more  or  less  pointed,  and  where  ad- 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  199 

vantage  is  taken  of  the  weight  of  the  body  and  the  shape  of 
the  pinion  to  utilize  the  air  as  a  supporting  medium.  In 
these  the  pinion  acts  as  a  long  lever,1  and  is  wielded  with 
great  precision  and  power,  particularly  at  the  shoulder. 

The  Flight  of  the  Albatross  compared  to  the  Movements  of  a 
Compass  set  upon  Gimbals. — A  careful  examination  of  the 
movements  in  skimming  birds  has  led  me  to  conclude  that 
by  a  judicious  twisting  or  screw-like  action  of  the  wings  at 
the  shoulder,  in  which  the  pinions  are  alternately  advanced 
towards  and  withdrawn  from  the  head  in  a  manner  analogous 
to  what  occurs  at  the  loins  in  skating  without  lifting  the 
feet,  birds  of  this  order  can  not  only  maintain  the  motion 
which  they  secure  by  a  few  energetic  flappings,  but,  if  neces- 
sary, actually  increase  it,  and  that  without  either  bending  the 
wing  or  beating  the  air. 

The  forward  and  backward  screwing  action  of  the  pinion 
referred  to,  in  no  way  interferes,  I  may  remark,  with  the  rota- 
tion of  the  wing  on  its  long  axis,  the  pinion  being  advanced 
and  screwed  down  upon  the  wind,  and  retracted  and  un- 
screwed alternately.  As  the  movements  described  enable 
the  sailing  bird  to  tilt  its  body  from  before  backwards,  or 

1  Advantages  possessed  by  long  Pinions. — The  long  narrow  wings  are  most 
effective  as  elevators  and  propellers,  from  the  fact  (pointed  out  by  Mr.  Wen- 
liam)  that  at  high  speeds,  with  very  oblique  incidences,  the  supporting  effect 
becomes  transferred  to  the/row^  edge  of  the  pinion.  It  is  in  this  way  "that 
the  effective  propelling  area  of  the  two-bladed  screw  is  tantamount  to  its 
entire  circle  of  revolution."  A  similar  principle  was  announced  by  Sir  George 
Cayley  upwards  of  fifty  years  ago.  "  In  very  acute  angles  with  the  current,  it 
appears  that  the  centre  of  resistance  in  the  sail  does  not  coincide  with  the 
centre  of  its  surface,  but  is  considerably  in  front  of  it.  As  the  obliquity  of 
the  current  decreases,  these  centres  approach,  and  coincide  when  the  current 
becomes  perpendicular  to  the  plane  ;  hence  any  heel  of  the  machine  backwards 
or  forwards  removes  the  centre  of  support  behind  or  before  the  point  of  sus- 
pension."— Nicholson's  Journal,  vol.  xxv.  p.  83.  When  the  speed  attained 
by  the  bird  is  greatly  accelerated,  and  the  stratum  of  air  passed  over  in  any  given 
time  enormously  increased,  the  support  afforded  by  the  air  to  the  inclined 
planes  formed  by  the  wings  is  likewise  augmented.  This  is  proved  by  the 
rapid  flight  of  skimming  or  sailing  birds  when  the  wings  are  moved  at  long 
intervals  and  very  leisurely.  The  same  principle  supports  the  skater  as  he 
rushes  impetuously  over  insecure  ice,  and  the  thin  flat  stone  projected  along 
the  surface  of  still  water.  The  velocity  of  the  movement  in  either  case  pre- 
vents sinking  by  not  giving  the  supporting  particles  time  to  separate. 


200 


ANIMAL  LOCOMOTION. 


the  converse,  and  from  side  to  side  or  laterally,  it  may  be 
represented  as  oscillating  on  one  of  two  centres,  as  shown 
at  fig.  105;  the  one  corresponding  with  the  long  axis  of 
the  body  (fig.  105,  ab),  the  other  with  the  long  axis  of  the 
wings  (c  d).  Between  these  two  extremes  every  variety  of 
sailing  and  gliding  motion  which  is  possible  in  the  mariner's 
compass  when  set  upon  gimbals  may  be  performed ;  so  that 
a  skimming  or  sailing  bird  may  be  said  to  possess  perfect 
command  over  itself  and  over  the  element  in  which  it  moves. 


— d 


Captain  Hutton  makes  the  following  remarkable  state- 
ment regarding  the  albatross  : — "  I  have  sometimes  watched 
narrowly  one  of  these  birds  sailing  and  wheeling  about  in  all 
directions  for  more  than  an  hour,  without  seeing  the  slightest 
movement  of  the  wings,  and  have  never  witnessed  anything 
to  equal  the  ease  and  grace  of  this  bird  as  he  sweeps  past, 
often  within  a  few  yards,  every  part  of  his  body  perfectly 
motionless  except  the  head  and  eye,  which  turn  slowly  and 
seem  to  take  notice  of  everything." l 

"  Tranquil  its  spirit  seem'd  and  floated  slow ; 
Even  in  its  very  motion  there  was  rest."  2 

As  an  antithesis  to  the   apparently  lifeless  wings  of  the 

1  "  On  some  of  the  Birds  inhabiting- the  Southern  Ocean." — Ibis,   2d  series, 
vol.  i.  1865. 

2  Professor  Wilson's  Sonnet,  "  A  Cloud,"  etc. 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  201 

albatross,  the  ceaseless  activity  of  those  of  the  humming-bird 
may  be  adduced.  In  those  delicate  and  exquisitely  beautiful 
birds,  the  wings,  according  to  Mr.  Gould,  move  so  rapidly 
when  the  bird  is  poised  before  an  object,  that  it  is  impossible 
for  the  eye  to  follow  each  stroke,  and  a  hazy  circle  of  indis- 
tinctness on  each  side  of  the  bird  is  all  that  is  perceptible. 
When  the  humming-bird  flies  in  a  horizontal  direction,  it 
occasionally  proceeds  with  such  velocity  as  altogether  to  elude 
observation. 

The  regular  and  irregular  in  Flight. — The  coot,  diver,  duck, 
and  goose  fly  with  great  regularity  in  nearly  a  straight  line, 
and  with  immense  speed ;  they  rarely  if  ever  skim  or  glide, 
their  wings  being  too  small  for  this  purpose.  The  wood- 
pecker, magpie,  fieldfare  and  sparrow,  supply  examples  of 
what  may  be  termed  the  "  irregular  "  in  flight.  These,  as  is 
well  known,  fly  in  curves  of  greater  or  less  magnitude, 
by  giving  a  few  vigorous  strokes  and  then  desisting,  the 
effect  of  which  is  to  project  them  along  a  series  of  para- 
bolic curves.  The  snipe  and  woodcock  are  irregular  in 
another  respect,  their  flight  being  sudden,  jerky,  and  from 
side  to  side. 

Mode  of  ascending,  descending,  turning,  etc. — All  birds  which 
do  not,  like  the  swallow  and  humming-birds,  drop  from  a 
height,  raise  themselves  at  first  by  a  vigorous  leap,  in  which 
they  incline  their  bodies  in  an  upward  direction,  the  height 
thus  attained  enabling  them  to  extend  and  depress  their 
wings  without  injury  to  the  feathers.  By  a  few  sweeping 
strokes  delivered  downwards  and  forwards,  in  which  the 
wings  are  made  nearly  to  meet  above  and  below  the  body, 
they  lever  themselves  upwards  and  forwards,  and  in  a  sur- 
prisingly short  time  acquire  that  degree  of  momentum  which 
greatly  assists  them  in  their  future  career.  In  rising  from 
the  ground,  as  may  readily  be  seen  in  the  crow,  pigeon, 
and  kingfisher  (fig.  102,  p.  183),  the  tail  is  expanded  and  the 
neck  stretched  out,  so  that  the  body  is  converted  into  an 
inclined  plane,  and  acts  mechanically  as  a  kite.  The  centre 
of  gravity  and  the  position  of  the  body  are  changed  at  the 
will  of  the  bird  by  movements  in  the  neck,  feet,  and  tail, 
and  by  increasing  or  decreasing  the  angles  which  the  under 

10 


202  ANIMAL  LOCOMOTION. 

surface  of  the  wings  makes  with  the  horizon.  When  a  bird 
wishes  to  fly  in  a  horizontal  direction,  it  causes  the  under 
surface  of  its  wings  to  make  a  slight  forward  angle  with  the 
horizon.  When  it  wishes  to  ascend,  the  angle  is  increased. 
When  it  wishes  to  descend,  it  causes  the  under  surface  of  the 
wings  to  make  a  slight  backward  angle  with  the  horizon. 
When  a  bird  flies  up,  its  wings  strike  downwards  and  forwards. 
When  it  flies  down,  its  wings  strike  downwards  and  backwards. 
When  a  sufficient  altitude  has  been  attained,  the  length  of 
the  downward  stroke  is  generally  curtailed,  the  mere  exten- 
sion and  flexion  of  the  wing,  assisted  by  the  weight  of  the 
body,  in  such  instances  sufficing.  This  is  especially  the  case 
if  the  bird  is  advancing  against  a  slight  breeze,  the  effort 
required  under  such  circumstances  being  nominal  in  amount. 
That  little  power  is  expended  is  proved  by  the  endless 
gyrations  of  rooks  and  other  birds;  these  being  continued 
for  hours  together.  In  birds  which  glide  or  skim,  it  has 
appeared  to  me  that  the  wing  is  recovered  much  more 
quickly,  and  the  down  stroke  delivered  more  slowly,  than 
in  ordinary  flight — in  fact,  that  the  rapidity  with  which  the 
wing  acts  in  an  upward  and  downward  direction  is,  in  some 
instances,  reversed;  and  this  is  what  we  should  naturally 
expect  when  we  recollect  that  in  gliding,  the  wings  require 
to  be,  for  the  most  part,  in  the  expanded  condition.  If 
this  observation  be  correct,  it  follows  that  birds  have  the 
power  of  modifying  the  duration  of  the  up  and  down  strokes 
at  pleasure.  Although  the  wing  of  the  bird  usually  strikes 
the  air  at  an  angle  which  varies  from  15°  to  30°,  the  angle 
may  be  increased  to  such  an  extent  as  to  subvert  the  position 
of  the  bird.  The  tumbler  pigeon,  e.g.  can,  by  slewing  its 
wings  forwards  and  suddenly  throwing  back  its  head,  turn 
a  somersault.  When  birds  are  fairly  on  the  wing  they  have 
the  air,  unless  when  that  is  greatly  agitated  by  a  storm, 
completely  under  control.  This  arises  from  their  greater 
specific  gravity,  and  because  they  are  possessed  of  independent 
motion.  If  they  want  to  turn,  they  have  simply  to  tilt  their 
bodies  laterally,  as  a  railway  carriage  would  be  tilted  in 
taking  a  curve,1  or  to  increase  the  number  of  beats  given  by 
1  "  If  the  albatross  desires  to  turn  to  the  right  he  bends  his  head  and  tail 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  203 

the  one  wing  as  compared  with  the  other ;  or  to  keep  the 
one  wing  extended  while  the  other  is  partially  flexed.  The 
neck,  feet,  and  tail  may  or  may  not  contribute  to  this  result. 
If  the  bird  wishes  to  rise,  it  tilts  its  entire  body  (the  neck 
and  tail  participating)  in  an  upward  direction  (fig.  5 9, p.  126  ; 
fig.  102,  p.  183) ;  or  it  rises  principally  by  the  action  of  the 
wings  and  by  muscular  efforts,  as  happens  in  the  lark.  The 
bird  can  in  this  manner  likewise  retain  its  position  in  the 
air,  as  may  be  observed  in  the  hawk  when  hovering  above 
its  prey.  If  the  bird  desires  to  descend,  it  may  reverse 
the  direction  of  the  inclined  plane  formed  by  the  body  and 
wings,  and  plunge  head  foremost  with  extended  pinions 


FIG.  106. — The  Pigeon  (Treron  bicincta,  Jerdon),  flying  downwards  and  turning 
prior  to  alighting.  The  pigeon  expands  its  tail  both  in  ascending  and 
descending.  —Original. 

(fig.  106)";  or  it  may  flex  the  wings,  and  so  accelerate  its 
pace ;  or  it  may  raise  its  wings  and  drop  parachute-fashion 
(fig.  55,  p.  112 ;  g,  g  of  fig.  82,  p.  158) ;  or  it  may  even  fly 
in  a  downward  direction — a  few  sudden  strokes,  a  more 
or  less  abrupt  curve,  and  a  certain  degree  of  horizontal 
movement  being  in  either  case  necessary  to  break  the 

slightly  upwards,  at  the  same  time  raising  his  left  side  and  wing,  and  lowering 
the  right  in  proportion  to  the  sharpness  of  the  curve  he  wishes  to  make,  the 
wings  being  kept  quite  rigid  the  whole  time.  To  such  an  extent  does  he  do 
this,  that  in  sweeping  round,  his  wings  are  often"pointed  in  a  direction  nearly 
perpendicular  to  the  sea  ;  and  this  position  of  the  wings,  more  or  less  inclined 
to  the  horizon,  is  seen  always  and  only  when  the  bird  is  turning." — "  On  some 
of  the  Birds  inhabiting  the  Southern  Ocean."  Ibis,  2d  series,  vol.  i.  1865, 
p.  227. 


204  ANIMAL  LOCOMOTION. 

fall  previous  to  alighting  (fig.  107,  below).  Birds  which 
fish  on  the  wing,  as  the  osprey  and  gannet,  precipitate 
themselves  from  incredible  heights,  and  drop  into  the  water 
with  the  velocity  of  a  meteorite — the  momentum  which 
they  acquire  during  their  descent  materially  aiding  them 
in  their  subaqueous  flight.  They  emerge  from  the  water 
and  are  again  upon  the  wing  before  the  eddies  occasioned 
by  their  precipitous  descent  have  well  subsided,  in  some  cases 
rising  apparently  without  effort,  and  in  others  running  along 
and  beating  the  surface  of  the  water  for  a  brief  period  with 
their  pinions  and  feet. 

The  Flight  of  Birds  referable  to  Muscular  Exertion  and  Weight. 
— The  various  movements  involved  in  ascending,  descending, 


FIG.  107.— The  Red-headed  Pochard  (Fuligula  ferina,  Linn.)  in  the  net  of  drop- 
ping upon  the  water ;  the  head  and  body  being  inclined  upwards  nnd  for- 
wards, the  feet  expanded,  and  the  wings  delivering  vigorous  short  strokes 
in  a  downward  and  forward  direction. — Original. 

wheeling,  gliding,  and  progressing  horizontally,  are  all  the 
result  of  muscular  power  and  weight,  properly  directed  and 
acting  upon  appropriate  surfaces — that  apparent  buoyancy  in 
birds  which  we  so  highly  esteem,  arising  not  from  superior- 
lightness,  but  from  their  possessing  that  degree  of  solidity 
which  enables  them  to  subjugate  the  air, — weight  and  inde- 
pendent motion,  i.e.  motion  associated  with  animal  life,  or 
what  is  equivalent  thereto,  being  the  two  things  indispensable 
in  successful  aerial  progression.  The  weight  in  insects  and 
birds  is  in  great  measure  owing  to  their  greatly  developed 
muscular  system,  this  being  in  that  delicate  state  of  tonicity 


PROGRESSION  IN  OR  THROUGH  THE  AIR.  205 

which  enables  them  to  act  through  its  instrumentality  with 
marvellous  dexterity  and  power,  and  to  expend  or  reserve 
their  energies,  which  they  can  do  with  the  utmost  exactitude, 
in  their  apparently  interminable  flights. 

Lifting-capacity  of  Birds. — The  muscular  power  in  birds  is 
usually  greatly  in  excess,  particularly  in  birds  of  prey,  as,  e.g. 
the  condors,  eagles,  hawks,  and  owls.  The  eagles  are  remark- 
able in  this  respect — these  having  been  known  to  carry  oft' 
young  deer,  lambs,  rabbits,  hares,  and,  it  is  averred,  even 
young  children.  Many  of  the  fishing  birds,  as  the  pelicans 
and  herons,  can  likewise  carry  considerable  loads  of  fish  ;x 
and  even  the  smaller  birds,  as  the  records  of  spring  show, 
are  capable  of  transporting  comparatively  large  twigs  for 
building  purposes.  I  myself  have  seen  an  owl,  which  weighed 
a  little  over  10  ounces,  lift  2^  ounces,  or  a  quarter  of  its  own 
weight,  without  effort,  after  having  fasted  twenty-four  hours ; 
and  a  friend  informs  me  that  a  short  time  ago  a  splendid 
osprey  was  shot  at  Littlehampton,  on  the  coast  of  Sussex, 
with  a  fish  5  Ibs.  weight  in  its  mouth. 

There  are  many  points  in  the  history  and  economy  of  birds 
which  crave  our  sympathy  while  they  elicit  our  admiration. 
Their  indubitable  courage  and  miraculous  powers  of  flight 
invest  them  with  a  superior  dignity,  and  secure  for  their 
order  almost  a  duality  of  existence.  The  swallow,  tiny  and 
inconsiderable  as  it  may  appear,  can  traverse  1000  miles  at  a 
single  journey;  and  the  albatross,  despising  compass  and  land- 
mark, trusts  himself  boldly  for  weeks  together  to  the  mercy 
or  fury  of  the  mighty  ocean.  The  huge  condor  of  the  Andes 
lifts  himself  by  his  sovereign  will  to  a  height  where  no  -sound 
is  heard,  save  the  airy  tread  of  his  vast  pinions,  and,  from  an 
unseen  point,  surveys  in  solitary  grandeur  the  wide  range  of 
plain  and  pasture-land  ;2  while  the  bald  eagle,  nothing 
daunted  by  the  din  and  indescribable  confusion  of  the  queen 
of  waterfalls,  the  stupendous  Niagara,  sits  composedly  on  his 


1  The  heron  is  in  the  habit,  when  pursued  by  the  falcon,  of  disgorging  the 
contents  of  his  crop  in  order  to  reduce  his  weight. 

2  The  condor,  on  some  occasions,  attains  an  altitude  of  six  miles. 


206 


ANIMAL  LOCOMOTION. 


giddy  perch,  until  inclination  or  desire  prompts  him  to  plunge 
into  or  soar  above  the  drenching  mists  which,  shapeless  and 
ubiquitous,  perpetually  rise  from  the  hissing  waters  of  the 
nether  caldron. 


FIG.  108.— Hawk  and  quarry.— After  The  Graphic. 


AERONAUTICS. 


THE  VAUXHALL  BALLOON  OF  MB.  GBEEN. 


AERONAUTICS. 

THE  subject  of  artificial  flight,  notwithstanding  the  large 
share  of  attention  bestowed  upon  it,  has  been  particularly 
barren  of  results.  This  is  the  more  to  be  regretted,  as  the 
interest  which  has  been  taken  in  it  from  early  Greek  and 
Roman  times  has  been  universal.  The  unsatisfactory  state  of 
the  question  is  to  be  traced  to  a  variety  of  causes,  the  most 
prominent  of  which  are — 

1st,  The  extreme  difficulty  of  the  problem. 

2d,  The  incapacity  or  theoretical  tendencies  of  those  who 
have  devoted  themselves  to  its  elucidation. 

3d,  The  great  rapidity  with  which  wings,  especially  insect 
wings,  are  made  to  vibrate,  and  the  difficulty  experienced  in 
analysing  their  movements. 

4th,  The  great  weight  of  all  flying  things  when  compared 
with  a  corresponding  volume  of  air. 

5th,  The  discovery  of  the  balloon,  which  has  retarded  the 
science  of  aerostation,  by  misleading  men's  minds  and  causing 
them  to  look  for  a  solution  of  the  problem  by  the  aid  of  a 
machine  lighter  than  the  air,  and  which  has  no  analogue  in 
nature. 

Flight  has  been  unusually  unfortunate  in  its  votaries.  It 
has  been  cultivated,  on  the  one  hand,  by  profound  thinkers, 
especially  mathematicians,  who  have  worked  out  innumer- 
able theorems,  but  have  never  submitted  them  to  the  test  of 
experiment ;  and  on  the  other,  by  uneducated  charlatans  who, 
despising  the  abstractions  of  science,  have  made  the  most  ridi- 
culous attempts  at  a  practical  solution  of  the  problem. 

Flight,  as  the  matter  stands  at  present,  may  be  divided 
into  two  principal  varieties  which  represent  two  great  sects 
or  schools — 


210  AERONAUTICS. 

1st,  The  Balloonists,  or  those  who  advocate  the  employ- 
ment of  a  machine  specifically  lighter  than  the  air. 

2d,  Those  who  believe  that  weight  is  necessary  to  flight. 
The  second  school  may  be  subdivided  into 

(a)  Those  who  advocate  the  employment  of  rigid  inclined 
planes  driven  forward  in  a  straight  line,  or  revolving 
planes  (aerial  screws)  ;  and 

.  (b)  Such  as  trust  for  elevation  and  propulsion  to  the 
vertical  flapping  of  wings. 

Balloon. — The  balloon,  as  my  readers  are  aware,  is  con- 
structed on  the  obvious  principle  that  a  machine  lighter  than 
the  air  must  necessarily  rise  through  it.  The  Montgolfier 
brothers  invented  such  a  machine  in  1782.  Their  balloon 
consisted  of  a  paper  globe  or  cylinder,  the  motor  power  being 
super-heated  air  supplied  by  the  burning  of  vine  twigs  under 
it  The  Montgolfier  or  fire  balloon,  as  it  was  called,  was 
superseded  by  the  hydrogen  gas  balloon  of  MM.  Charles 
and  Robert,  this  being  in  turn  supplanted  by  the  ordinary  gas 
balloon  of  Mr.  Green.  Since  the  introduction  of  coal  gas  in 
the  place  of  hydrogen  gas,  no  radical  improvement  has  been 
effected,  all  attempts  at  guiding  the  balloon  having  signally 
failed.  This  arises  from  the  vast  extent  of  surface  which  it 
necessarily  presents,  rendering  it  a  fair  conquest  to  every 
breeze  that  blows ;  and  because  the  power  which  animates  it 
is  a  mere  lifting  power  which,  in  the  absence  of  wind,  must 
act  in  a  vertical  line.  The  balloon  consequently  rises  through 
the  air  in  opposition  to  the  law  of  gravity,  very  much  as  a 
dead  bird  falls  in  a  downward  direction  in  accordance  with 
it.  Having  no  hold  upon  the  air,  this  cannot  be  employed  as 
a  fulcrum  for  regulating  its  movements,  and  hence  the  car- 
dinal difficulty  of  ballooning  as  an  art. 

Finding  that  no  marked  improvement  has  been  made  in 
the  balloon  since  its  introduction  in  1782,  the  more  advanced 
thinkers  have  within  the  last  quarter  of  a  century  turned 
their  attention  in  an  opposite  direction,  and  have  come  to 
regard  flying  creatures,  all  of  which  are  much  heavier  than 
the  air,  as  the  true  models  for  flying  machines.  An  old 
doctrine  is  more  readily  assailed  than  uprooted,  and  accord- 
ingly we  find  the  followers  of  the  new  faith  met  by  the 
assertion  that  insects  and  birds  have  large  air  cavities  in 


AERONAUTICS.  211 

their  interior ;  that  those  cavities  contain  heated  air,  and  that 
this  heated  air  in  some  mysterious  manner  contributes  to,  if 
it  does  not  actually  produce,  flight.  No  argument  could  be 
more  fallacious.  Many  admirable  fliers,  such  as  the  bats, 
have  no  air-cells ;  while  many  birds,  the  apteryx  for  example, 
and  several  animals  never  intended  to  fly,  such  as  the  orang- 
outang and  a  large  number  of  fishes,  are  provided  with  them. 
It  may  therefore  be  reasonably  concluded  that  flight  is  in  no 
way  connected  with  air-cells,  and  the  best  proof  that  can  be 
adduced  is  to  be  found  in  the  fact  that  it  can  be  performed 
to  perfection  in  their  absence. 

The  Inclined  Plane. — The  modern  school  of  flying  is  in 
some  respects  quite  as  irrational  as  the  ballooning  school. 

The  favourite  idea  with  most  is  the  wedging  forward  of  a 
rigid  inclined  plane  upon  the  air  by  means  of  a,  "vis  a  tergo." 

The  inclined  plane  may  be  made  to  advance  in  a  horizontal 
line,  or  made  to  rotate  in  the  form  of  a  screw.  Both  plans 
have  their  adherents.  The  one  recommends  a  large  support- 
ing area  extending  on  either  side  of  the  weight  to  be  elevated; 
the  surface  of  the  supporting  area  making  a  very  slight  angle 
with  the  horizon,  and  the  whole  being  wedged  forward  by  the 
action  of  vertical  screw  propellers.  This  was  the  plan  sug- 
gested by  Henson  and  Stringfellow. 

Mr.  Henson  designed  his  aerostat  in  1843.  "The  chief 
feature  of  the  invention  was  the  very  great  expanse  of  its 
sustaining  planes,  which  were  larger  in  proportion  to  the 
weight  it  had  to  carry  than  those  of  many  birds.  The 
machine  advanced  with  its  front  edge  a  little  raised,  the 
effect  of  which  was  to  present  its  under  surface  to  the  air 
over  which  it  passed,  the  resistance  of  which,  acting  upon  it 
like  a  strong  wind  on  the  sails  of  a  windmill,  prevented  the 
descent  of  the  machine  and  its  burden.  The  sustaining  of 
the  whole,  therefore,  depended  upon  the  speed  at  which  it 
travelled  through  the  air,  and  the  angle  at  which  its  under 
surface  impinged  on  the  air  in  its  front.  .  .  .  The  machine, 
fully  prepared  for  flight,  was  started  from  the  top  of  an 
inclined  plane,  in  descending  which  it  attained  a  velocity 
necessary  to  sustain  it  in  its  further  progress.  That  velocity 
would  be  gradually  destroyed  by  the  resistance  of  the  air  to 
forward  flight;  it  was,  therefore,  the  office  of  the  steam- 


212  AERONAUTICS. 

engine  and  the  vanes  it  actuated  simply  to  repair  the  loss  of 
velocity ;  it  was  made  therefore  only  of  the  power  and  weight 
necessary  for  that  small  effect "  (fig.  109).  The  editor  of  New- 
ton's Journal  of  Arts  and  Science  speaks  of  it  thus  : — "  The 
apparatus  consists  of  a  car  containing  the  goods,  passengers, 
engines,  fuel,  etc.,  to  which  a  rectangular  frame,  made  of 
wood  or  bamboo  cane,  and  covered  with  canvas  or  oiled  silk, 
is  attached.  This  frame  extends  on  either  side  of  the  car  in 
a  similar  manner  to  the  outstretched  wings  of  a  bird ;  but 
with  this  difference,  that  the  frame  is  im'movalle.  Behind 
the  wings  are  two  vertical  fan  wheels,  furnished  with  oblique 


Fio.  109.  — Mr.  Benson's  Flying  Machine. 

vanes,  which  are  intended  to  propel  the  apparatus  through 
the  air.  The  rainbow-like  circular  wheels  are  the  propellers, 
answering  to  the  wheels  of  a  steam-boat,  and  acting  upon  the 
air  after  the  manner  of  a  windmill.  These  wheels  receive 
motion  from  bands  and  pulleys  from  a  steam  or  other  engine 
contained  in  the  car.  To  an  axis  at  the  stern  of  the  car  a 
triangular  frame  is  attached,  resembling  the  tail  of  a  bird, 
which  is  also  covered  with  canvas  or  oiled  silk.  This  may 
be  expanded  or  contracted  at  pleasure,  and  is  moved  up  and 
down  for  the  purpose  of  causing  the  machine  to  ascend  or 
descend.  Beneath  the  tail  is  a  rudder  for  directing  the 
course  of  the  machine  to  the  right  or  to  the  left;  and  to 
facilitate  the  steering  a  sail  is  stretched  between  two  masts 
which  rise  from  the  car.  The  amount  of  canvas  or  oiled  silk 
necessary  for  buoying  up  the  machine  is  stated  to  be  equal 
to  one  square  foot  for  each  half  pound  of  weight." 


AERONAUTICS. 


213 


"Wenham1  has  advocated  the  employment  of  superimposed 
planes,  with  a  view  to  augmenting  the  support  furnished 
Avhile  it  diminishes  the  horizontal  space  occupied  by  the 
planes.  These  planes  Wenham  designates  Aeroplanes.  They 
are  inclined  at  a  very  slight  angle  to  the  horizon,  and  are 
wedged  forward  either  by  the  weight  to  be  elevated  or  by  the 
employment  of  vertical  screws.  Weuham's  plan  was  adopted 
by  Stringfellow  in  a  model  which  he  exhibited  at  the  Aero- 
nautical Society's  Exhibition,  held  at  the  Crystal  Palace  in 
the  summer  of  1868. 

The  subjoined  woodcut  (fig.  110),  taken  from  a  photograph 


FIG.  110.— Mr.  Stringfellow's  Flying  Machine. 

of  Mr.  Stringfellow's  model,  gives  a  very  good  idea  of  the 
arrangement ;  ab  c  representing  the  superimposed  planes,  d 
the  tail,  and  e/the  vertical  screw  propellers. 

The  superimposed  planes  (a  b  c)  in  this  machine  contained 
a  sustaining  area  of  twenty-eight  square  feet  in  addition  to 
the  tail  (il). 

Its  engine  represented  a  third  of  a  horse  power,  and  the 

weight  of  the  whole  (engine,  boiler,  water,  fuel,  superimposed 

planes,   and  propellers)   was  under  12  Ibs.      Its   sustaining 

area,  if  that  of  the  tail  (d)  be  included,  was  something  like 

thirty- six  square  feet,  i.e.  three  square  feet  for  every  pound 

» — the  sustaining  area  of  the  gannet,  it  will  be  remembered 

(p.  134),  being  less  than  one  square  foot  of  wing  for  every 

two  pounds  of  body. 

i  "Aerial  Locomotion,"  by  F.  H.  Wenham.—  World  of  Science,  June  1867. 


214  AERONAUTICS. 

The  model  was  forced  by  its  propellers  along  a  wire  at  a 
great  speed,  but,  so  far  as  I  could  determine  from  observa- 
tion, failed  to  lift  itself  notwithstanding  its  extreme  lightness 
and  the  comparatively  very  great  power  employed.1 

The  idea  embodied  by  Henson,  Wenham,  and  Striqgfellow 
is  plainly  that  of  a  boy's  kite  sailing  upon  the  wind.  The 
kite,  however,  is  a  more  perfect  flying  apparatus  than  that 
furnished  by  Henson,  Wenham,  and  Stringfellow,  inasmuch 
as  the  inclined  plane  formed  by  its  body  strikes  the  air  at 
various  angles — the  angles  varying  according  to  the  length  of 
string,  strength  of  breeze,  length  and  weight  of  tail,  etc. 
Henson's,  Wenham's,  and  Stringfellow's  methods,  although 
carefully  tried,  have  hitherto  failed.  The  objections  are 
numerous.  In  the  first  place,  the  supporting  planes  (aero- 
planes or  otherwise)  are  not  flexible  and  elastic  as  wings 
are,  but  rigid.  This  is  a  point  to  which  I  wish  particularly 
to  direct  attention.  Second,  They  strike  the  air  at  a  given 
angle.  Here,  again,  there  is  a  departure  from  nature.  Third, 
A  machine  so  constructed  must  be  precipitated  from  a  height 
or  driven  along  the  surface  of  the  land  or  water  at  a  high 
speed  to  supply  it  with  initial  velocity.  Fourth,  It  is  un- 
fitted for  flying  with  the  wind  unless  its  speed  greatly  exceeds 
that  of  the  wind.  Fifth,  It  is  unfitted  for  flying  across 
the  wind  because  of  the  surface  exposed.  Sixth,  The  sus- 
taining surfaces  are  comparatively  very  large.  They  are, 
moreover,  passive  or  dead  surfaces,  i.e.  they  have  no  power 
of  moving  or  accommodating  themselves  to  altered  circum- 
stances. Natural  wings,  on  the  contrary,  present  small  flying 
surfaces,  the  great  speed  at  which  wings  are  propelled  con- 
verting the  space  through  which  they  are  driven  into  what 
is  practically  a  solid  basis  of  support,  as  explained  at  pp.  118, 
119,  151,  and  152  (vide  figs.  64,  65,  66,  82,  and  83,  pp.  139 
and  158).  This  arrangement  enables  natural  wings  to  seize 
and  utilize  the  air,  and  renders  them  superior  to  adventitious 
currents.  Natural  wings  work  up  the  air  in  which  they  move, 
but  unless  the  flying  animal  desires  it,  they  are  scarcely,  if  at 
all,  influenced  by  winds  or  currents  which  are  not  of  their 
own  forming.  In  this  respect  they  entirely  differ  from  the 

1  Mr.  Stringfellow  stated  that  his  machine  occasionally  left  the  wire,  and 
was  sustained  by  its  superimposed  planes  alone. 


AERONAUTICS.  215 

balloon  and  all  forms  of  fixed  aeroplanes.  In  nature,  small 
wings  driven  at  a  high  speed  produce  the  same  result  as  large 
wings  driven  at  a  slow  speed  (compare  fig.  58,  p.  125,  with 
fig.  57,  p.  124).  In  flight  a  certain  space  must  be  covered 
either  by  large  wings  spread  out  as  a  solid  (fig.  57,  p.  124),  or 
by.small  wings  vibrating  rapidly  (figs.  64,  65,  and  66,  p.  139). 


Fio.  111.— Caylcy's  Flying  Apparatus. 

The  Aerial  Screw. — Our  countryman,  Sir  George  Cayley, 
gave  the  first  practical  illustration  of  the  efficacy  of  the  screw 
as  applied  to  the  air  in  1796.  In  that  year  he  constructed  a 
small  machine,  consisting  of  two  screws  made  of  quill  feathers 
(fig.  111).  Sir  George  writes  as  under  : — 

"•As  it  may  be  an  amusement  to  some  of  your  readers  to 
see  a  machine  rise  in  the  air  by  mechanical  means,  I  will  con- 


216  AERONAUTICS. 

elude  my  present  communication  by  describing  an  instrument 
of  this  kind,  which  any  one  can  construct  at  the  expense  of 
ten  minutes'  labour. 

"  a  and  b  (fig.  1 1 1 ,  p.  2 1 5)  are  two  corks,  into  each  of  which 
are  inserted  four  wing  feathers  from  any  bird,  so  as  to  be  slightly 
inclined  like  the  sails  of  a  windmill,  but  in  opposite  directions 
in  each  set.  A  round  shaft  is  fixed  in  the  cork  a,  which  ends 
in  a  sharp  point.  At  the  upper  part  of  the  cork  b  is  fixed  a 
whalebone  bow,  having  a  small  pivot  hole  in  its  centre  to 
receive  the  point  of  the  shaft.  The  bow  is  then  to  be  strung 
equally  on  each  side  to  the  upper  portion  of  the  shaft,  and 
the  little  machine  is  completed.  Wind  up  the  string  by 
turning  the  flyers  different  ways,  so  that  the  spring  of  the 
bow  may  unwind  them  with  their  anterior  edges  ascending ; 
then  place  the  cork  with  the  bow  attached  to  it  upon  a  table, 
and  with  a  finger  on  the  upper  cork  press  strong  enough  to 
prevent  the  string  from  unwinding,  and,  taking  it  away  sud- 
denly, the  instrument  will  rise  to  the  ceiling." 

Cayley's  screws  were  peculiar,  inasmuch  as  they  were  super- 
imposed and  rotated  in  opposite  directions.  He  estimated 
that  if  the  area  of  the  screws  was  increased  to  200  square 
feet,  and  moved  by  a  man,  they  would  elevate  him.  Cayley's 
interesting  experiment  is  described  at  length,  and  the  ap- 
paratus figured  in  Nicholson's  Journal  for  1809,  p.  172.  In 
1842  Mr.  Phillips  also  succeeded  in  elevating  a  model  by 
means  of  revolving  fans.  Mr.  Phillips's  model  was  made 
entirely  of  metal,  and  when  complete  and  charged  weighed 
2  Ibs.  It  consisted  of  a  boiler  or  steam  generator  and  four 
fans  supported  between  eight  arms.  The  fans  were  inclined 
to  the  horizon  at  an  angle  of  20°,  and  through  the  arms  the 
steam  rushed  on  the  principle  discovered  by  Hero  of  Alexan- 
dria. By  the  escape  of  steam  from  the  arms,  the  fans  were 
made  to  revolve  with  immense  energy,  so  much  so  that  the 
model  rose  to  a  great  altitude,  and  flew  across  two  -fields 
before  it  alighted.  The  motive  power  employed  in  the  pre- 
sent instance  was  obtained  from  the  combustion  of  charcoal, 
nitre,  and  gypsum,  as  used  in  the  original  fire  annihilator ; 
the  products  of  combustion  mixing  with  water  in  the  boiler, 
and  forming  gas  charged  steam,  which  was  delivered  at  a 
high  pressure  from  the  extremities  of  the  eight  arms.  This 


AERONAUTICS. 


217 


model  is  remarkable  as  being  probably  the  first  which  actuated 
by  steam  has  flown  to  a  considerable  distance.1  The  French 
have  espoused  the  aerial  screw  with  great  enthusiasm,  and 
within  the  last  ten  years  (1863)  MM.  Nadar,2  Pontin 


FIG.  112. — Flying  Machine  designed  by  M.  de  la  Landelle. 

d'Amecourt,  and  de  la  Landelle  have  constructed  clockwork 
models  (ortlwpteres) ,  which  not  only  raise  themselves  into  the 
air,  but  carry  a  certain  amount  of  freight.  These  models  are 

1  Report  on  the  First  Exhibition  of  the  Aeronautical  Society  of  Great 
Britain,  held  at  the  Crystal  Palace,  London,  in  June  1868,  p.  10. 

2  Mons.  Nadar,  in  a  paper  written  in  1863,  enters  very  fully  into  the  sub- 
ject of  artificial  flight,  as  performed  by  the  aid  of  the  screw.    Liberal  extracts 
are  given  from  Nadar's  paper  in  Astra  Castra,  by  Captain  Hatton  Turner. 
London,  1865,  p.  340.     To  Turner's  handsome  volume  the  reader  is  referred 
for  much  curious  and  interesting  information  on  the  subject  of  Aerostation. 


218  AERONAUTICS. 

exceedingly  fragile,  and  because  of  the  prodigious  force 
required  to  propel  them  usually  break  after  a  few  trials. 
Fig.  112,  p.  217,  embodies  M.  de  la  Landelle's  ideas. 

In  the  helicopteric  models  made  by  MM.  Nadar,  Pontin 
d'Am6court,  and  de  la  Landelle,  the  screws  (mnopqrst  of 
figure)  are  arranged  in  tiers,  i.e.  the  one  screw  is  placed 
above  the  other.  In  this  respect  they  resemble  the  aero- 
planes recommended  by  Mr.  Wenham,  and  tested  by  Mr. 
Stringfellow  (compare  mnop  qrst  of  fig.  112,  with  abc  of 
fig.  110,  p.  213).  The  superimposed  screws,  as  already 
explained,  were  first  figured  and  described  by  Sir  George 
Cayley  (p.  215).  The  French  screws,  and  that  employed  by 
Mr.  Phillips,  are  rigid  or  unyielding,  and  strike  the  air  at  a 
given  angle,  and  herein,  I  believe,  consists  their  principal 
defect.  This  arrangement  results  in  a  ruinous  expenditure  of 
power,  and  is  accompanied  by  a  great  amount  of  slip.  The 
aerial  screw,  and  the  machine  to  be  elevated  by  it,  can  be  set 
in  motion  without  any  preliminary  run,  and  in  this  respect  it 
has  the  advantage  over  the  machine  supported  by  mere  sus- 
taining planes.  It  has,  in  fact,  a  certain  amount  of  inherent 
motion,  its  screws  revolving,  and  supplying  it  with  active  or 
moving  surfaces.  It  is  accordingly  more  independent  than 
the  machine  designed  by  Henson,  Wenham,  and  Stringfellow. 

I  may  observe  with  regard  to  the  system  of  rigid  inclined 
planes  wedged  forward  at  a  given  angle  in  a  straight  line  or 
in  a  circle,  that  it  does  not  embody  the  principle  carried  out 
in  nature. 

The  wing  of  a  flying  creature,  as  I  have  taken  pains  to 
show,  is  not  rigid ;  neither  does  it  always  strike  the  air  at 
a  given  angle.  On  the  contrary,  it  is  capable  of  moving  in 
all  its  parts,  and  attacks  the  air  at  an  infinite  variety  of 
angles  (pp.  151  to  154).  Above  all,  the  surface  exposed  by 
a  natural  wing,  when  compared  with  the  great  weight 
it  is  capable  of  elevating,  is  remarkably  small  (fig.  89, 
p.  171).  This  is  accounted  for  by  the  length  and  the  great 
range  of  motion  of  natural  wings;  the  latter  enabling  the 
wings  to  convert  large  tracts  of  air  into  supporting  areas  (figs. 
64,  65,  and  66,  p.  139).  It  is  also  accounted  for  by  the 
multiplicity  of  the  movements  of  natural  wings,  these  enabling 
the  pinions  to  create  and  rise  upon  currents  of  their  own 


AERONAUTICS.  219 

forming,  and  to  avoid  natural  currents  when  not  adapted  for 
propelling  or  sustaining  purposes  (fig.  67,«.68,  69,  and  70, 
p.  HI). 

If  any  one  watches  an  insect,  a  bat,  or  a  bird  when  dressing 
its  wings,  he  will  observe  that  it  can  incline  the  under  sur- 
face of  the  wing  at  a  great  variety  of  angles  to  the  horizon. 
This  it  does  by  causing  the  posterior  or  thin  margin  of  the 
wing  to  rotate  around  the  anterior  or  thick  margin  as  an 
axis.  As  a  result  of  this  movement,  the  two  margins  are 
forced  into  double  and  opposite  curves,  and  the  wing  con- 
verted into  a  plastic  helix  or  screw.  He  will  further  observe 
that  the  bat  and  bird,  and  some  insects,  have,  in  addition,  the 
power  of  folding  and  drawing  the  wing  towards  the  body 
during  the  up  stroke,  and  of  pushing  it  away  from  the  body 
and  extending  it  during  the  down  stroke,  so  as  alternately  to 
diminish  and  increase  its  area;  arrangements  necessary  to 
decrease  the  amount  of  resistance  experienced  by  the  wing 
during  its  ascent,  and  increase  it  during  its  descent.  It  is 
scarcely  requisite  to  add,  that  in  the  aeroplanes  and  aerial 
screws,  as  at  present  constructed,  no  provision  whatever  is 
made  for  suddenly  increasing  or  diminishing  the  flying  sur- 
face, of  conferring  elasticity  upon  it,  or  of  giving  to  it  that 
infinite  variety  of  angles  which  would  enable  it  to  seize 
and  disentangle  itself  from  the  air  with  the  necessary 
rapidity.  Many  investigators  are  of  opinion  that  flight  is 
a  mere  question  of  levity  and  power,  and  that  if  a  machine 
could  only  be  made  light  enough  and  powerful  enough, 
it  must  of  necessity  fly,  whatever  the  nature  of  its  flying 
surfaces.  A  grave  fallacy  lurks  here.  Birds  are  not  more 
powerful  than  quadrupeds  of  equal  size,  and  Stringfellow's 
machine,  which,  as  we  have  seen,  only  weighed  12  Ibs., 
exerted  one-third  of  a  horse  power.  The  probabilities  there- 
fore are,  that  flight  is  dependent  to  a  great  extent  on  the 
nature  of  the  flying  surfaces,  and  the  mode  of  applying  those 
surfaces  to  the  air. 

Artificial  Wings  (Borelli's  Views). — With  regard  to  .the 
production  of  flight  by  the  flapping  of  wings,  much  may  and 
has  been  said.  Of  all  the  methods  yet  proposed,  it  is  unques- 
tionably by  far  the  most  ancient.  Discrediting  as  apocryphal 
the  famous  story  of  Daedalus  and  his  waxen  wings,  we  cer- 


220 


AERONAUTICS. 


tainly  have  a  very  graphic  account  of  artificial  wings  in  the 
De  Motu  Animalium  of  Borelli,  published  as  far  back  as 
1680,  i.e.  nearly  two  centuries  ago.1 

Indeed  it  will  not  be  too  much  to  affirm,  that  to  this  dis- 
tinguished physiologist  and  mathematician  belongs  almost  all 
the  knowledge  we  possessed  of  artificial  wings  up  till  1865. 
He  was  well  acquainted  with  the  properties  of  the  wedge,  as 
applied  to  flight,  and  he  was  likewise  cognisant  of  the  flexible 
and  elastic  properties  of  the  wing.  To  him  is  to  be  traced 
the  purely  mechanical  theory  of  the  wing's  action.  He  figured 
a  bird  with  artificial  wings,  each  wing  consisting  of  a  rigid 
rod  in  front  and  flexible  feathers  behind.  I  have  thought  fit 
to  reproduce  Borelli's  figure  both  because  of  its  great  antiquity, 
and  because  it  is  eminently  illustrative  of  his  text.2 


FIG.  113.— Borelli's  Artificial  Bird. 

The  wings  (b  cf,  oca),  are  represented  as  striking  vertically 
downwards  (g  h).  They  remarkably  accord  with  those  de- 
scribed by  Straus-Durckheim,  Girard,  and  quite  recently  by 
Professor  Marey.3 

Borelli  is  of  opinion  that  flight  results  from  the  application 
of  an  inclined  plane,  which  beats  the  air,  and  which  has  a 
wedge  action.  He,  in  fact,  endeavours  to  prove  that  a  bird 
Avedges  itself  forward  upon  the  air  by  the  perpendicular  vibra- 

1  Borelli,  De  Motu  Animalium.     Sm.  4to,  2  vols.     Romae,  1680. 

2  De  Motu  Animalium,  Lugduni  Batavorum  apud  Petrum  Vander.     Anno 
MDCLXXXV.  Tab.  XIII.  figure  2.     (New  edition.) 

*  Revue  des  Cotirs  Scientifiques  de  la  France  et  de  1'Etranger.    Mars  1869. 


A&IONAUTICS.  221 

tion  of  its  wings,  the  wings  during  their  action  forming  a 
wedge,  the  base  of  which  (c  b  e)  is  directed  towards  the  head 
of  the  bird ;  the  apex  (af)  being  directed  towards  the  tail. 
This  idea  is  worked  out  in  propositions  195  and  196  of  the 
first  part  of  Borelli's  book.  In  proposition  195  he  explains 
how,  if  a  wedge  be  driven  into  a  body,  the  wedge  will  tend 
to  separate  that  body  into  two  portions ;  but  that  if  the  two 
portions  of  the  body  be  permitted  to  react  upon  the  wedge, 
they  will  communicate  oblique  impulses  to  the  sides  of  the 
wedge,  and  expel  it,  base  first,  in  a  straight  line. 

Following  up  the  analogy,  Borelli  endeavours  to  show  in 
his  196th  proposition,  "  that  if  the  air  acts  obliquely  upon 
the  wings,  or  the  wings  obliquely  upon  the  air  (which  is,  of 
course,  a  wedge  action),  the  result  will  be  a  horizontal  trans- 
ference of  the  body  of  the  bird."  In  the  proposition  referred  to 
(196)  Borelli  states — "  If  the  expanded  wings  of  a  bird  sus- 
pended in  the  air  shall  strike  the  undisturbed  air  beneath  it 
with  a  motion  perpendicular  to  the  horizon,  the  bird  will  fly 
with  a  transverse  motion  in  a  plane  parallel  with  the  horizon." 
In  other  words,  if  the  wings  strike  vertically  downwards,  the 
bird  will  fly  horizontally  foi'wards.  He  bases  his  argument 
upon  the  belief  that  the  anterior  margins  of  the  wings  are 
rigid  and  unyielding,  whereas  the  posterior  and  after  parts  of 
the  wings  are  mwe  or  less  flexible,  and  readily  give  way  under 
pressure.  "  If,"  he  adds,  "  the  wings  of  the  bird  be  expanded, 
and  the  under  surfaces  of  the  wings  be  struck  by  the  air 
ascending  perpendicularly  to  the  horizon,  with  such  a  force 
as  shall  prevent  the  bird  gliding  downwards  (i.e.  with  a 
tendency  to  glide  downwards)  from  falling,  it  will  be  urged 
in  a  horizontal!  direction.  This  follows  because  the  two 
osseous  rods  (virgse)  forming  the  anterior  margins  of  the 
wings  resist  the  upward  pressure  of  the  air,  and  so  retain 
their  original  form  (literally  extent  or  expansion),  whereas 
the  flexible  after-parts  of  the  wings  (posterior  margins)  are 
pushed  up  and  approximated  to  form  a  cone,  the  apex  of 
which  (vide  af  of  fig.  1 13)  is  directed  towards  the  tail  of  the 
bird.  In  virtue  of  the  air  playing  upon  and  compressing  the 
sides  of  the  wedge  formed  by  the  wings,  the  wedge  is  driven 
forwards  in  the  direction  of  its  base  (c  b  e),  which  is  equiva- 


222  AERONAUTICS. 

lent  to  saying  that  the  wings  carry  the  body  of  the  bird  to 
which  they  are  attached  in  a  horizontal  direction" 

Borelli  restates  the  same  argument  in  different  words,  as 
follows : — 

"  If,"  he  says,  "  the  air  under  the  wings  be  struck  by  the 
flexible  portions  of  the  wings  (flabella,  literally  fly-flaps  or 
small  fans)  with  a  motion  perpendicular  to  the  horizon,  the 
sails  (vela)  and  flexible  portions  of  the  wings  (flabella)  will 
yield  in  an  upward  direction,  and  form  a  wedge,  the  point  of 
which  is  directed  towards  the  tail.  Whether,  therefore,  the 
air  strikes  the  wings  from  below,  or  the  wings  strike  the  air 
from  above,  the  result  is  the  same — :the  posterior  or  flexible 
margins  of  the  wings  yield  in  an  upward  direction,  and  in 
so  doing  urge  the  bird  in  a  horizontal  direction." 

In  his  197th  proposition,  Borelli  follows  up  and  amplifies 
the  arguments  contained  in  propositions  195  and  196.  "  Thus," 
he  observes,  "  it  is  evident  that  the  object  of  flight  is  to 
impel  birds  upwards,  and  keep  them  suspended  in  the  air, 
and  also  to  enable  them  to  wheel  round  in  a  plane  parallel  to 
the  horizon.  The  first  (or  upward  flight)  could  not  be  accom- 
plished unless  the  bird  were  impelled  upwards  by  frequent 
leaps  or  vibrations  of  the  wings,  and  its  descent  prevented. 
And  because  the  downward  tendency  of  heavy  bodies  is  per- 
pendicular to  the  horizon,  the  vibration  of  the  plain  surfaces 
of  the  wings  must  be  made  by  striking  the  air  beneath  them 
in  a  direction  perpendicular  to  the  horizon,  and  in  this  man- 
ner nature  produces  the  suspension  of  birds  in  the  air." 

"  With  regard  to  the  second  or  transverse  motion  of  birds 
(i.e.  horizontal  flight)  some  authors  have  strangely  blundered; 
for  they  hold  that  it  is  like  that  of  boats,  which,  being  im- 
pelled by  oars,  moved  horizontally  in  the  direction  of  the 
stern,  and  pressing  on  the  resisting  water  behind,  leaps  with 
a  contrary  motion,  and  so  are  carried  forward.  In  the  same 
manner,  say  they,  the  wings  vibrate  towards  the  tail  with  a 
horizontal  motion,  and  likewise  strike  against  the  undisturbed 
air,  by  the  resistance  of  which  they  are  moved  forward  by  a 
reflex  motion.  But  this  is  contrary  to  the  evidence  of  our 
sight  as  well  as  to  reason ;  for  we  see  that  the  larger  kinds 
of  birds,  such  as  swans,  geese,  etc.,  never  vibrate  their  wings 


AERONAUTICS.  223 

when  flying  towards  the  tail  with  a  horizontal  motion  like 
that  of  oars,  but  always  bend  them  downwards,  and  so  describe 
circles  raised  perpendicularly  to  the  horizon.1 

Besides,  in  boats  the  horizontal  motion  of  the  oars  is  easily 
made,  and  a  perpendicular  stroke  on  the  water  would  be  per- 
fectly useless,  inasmuch  as  their  descent  would  be  impeded 
by  the  density  of  the  water.  But  in  birds,  such  a  horizontal 
motion  (which  indeed  would  rather  hinder  flight)  would  be 
absurd,  since  it  would  cause  the  ponderous  bird  to  fall  head- 
long to  the  earth ;  whereas  it  can  only  be  suspended  in  the 
air  by  constant  vibration  of  the  wings  perpendicular  to  the 
horizon.  Nature  was  thus  forced  to  show  her  marvellous  skill 
in  producing  a  motion  which,  by  one  and  the  same  action, 
should  suspend  the  bird  in  the  air,  and  carry  it  forward  in  a 
horizontal  direction.  This  is  effected  by  striking  the  air 
below  perpendicularly  to  the  horizon,  but  with  oblique 
strokes — an  action  which  is  rendered  possible  only  by  the 
flexibility  of  the  feathers,  for  the  fans  of  the  wings  in  the  act 
of  striking  acquire  the  form  of  a  wedge,  by  the  forcing  out  of 
which  the  bird  is  necessarily  moved  forwards  in  a  horizontal 
direction." 

The  points  which  Borelli  endeavours  to  establish  are 
these  : — 

First,  That  the  action  of  the  wing  is  a  wedge  action. 

Second,  That  the  wing  consists  of  two  portions — a  rigid 
anterior  portion,  and  a  non-rigid  flexible  portion.  The  rigid 
portion  he  represents  in  his  artificial  bird  (fig.  113,  p.  220)  as 
consisting  of  a  rod  (e  r\  the  yielding  portion  of  feathers  (a  o). 

Third,  That  if  the  air  strikes  the  under  surface  of  the 
wing  perpendicularly  in  a  direction  from  below  upwards,  the 
flexible  portion  of  the  wing  will  yield  in  an  upward  direction, 
and  form  a  wedge  with  its  neighbour. 

Fourth,  Similarly  and  conversely,  if  the  wing  strikes  the 

1  It  is  clear  from  the  above  that  Borelli  did  not  know  that  the  wings  of 
birds  strike  forwards  as  well  as  downwards  during  the  down  stroke,  and  for- 
wards as  well  as  upwards  during  the  up  stroke.  These  points,  as  well  as  the 
twisting  and  untwisting  figure-of-8  action  of  the  wing,  were  first  described  by 
the  author.  Borelli  seems  to  have  been  equally  ignorant  of  the  fact  that  the 
winces  of  insects  vibrate  in  a  more  or  less  horizontal  direction. 


224  AERONAUTICS. 

air  perpendicularly  from  above,  the  posterior  and  flexible 
portion  of  the  wing  will  yield  and  be  forced  in  an  upward 
direction. 

Fifth,  That  this  upward  yielding  of  the  posterior  or  flexible 
margin  of  the  wing  results  in  and  necessitates  a  horizontal 
transference  of  the  body  of  the  bird. 

Sixth,  That  to  sustain  a  bird  in  the  air  the  wings  must 
strike  vertically  downwards,  as  this  is  the  direction  in  which  a 
heavy  body,  if  left  to  itself,  would  fall. 

Seventh,  That  to  propel  the  bird  in  a  horizontal  direction, 
the  wings  must  descend  in  a  perpendicular  direction,  and  the 
posterior  or  flexible  portions  of  the  wings  yield  in  an  upward 
direction,  and  in  such  a  manner  as  virtually  to  communicate 
an  oblique  action  to  them. 

Eighth,  That  the  feathers  of  the  wing  are  lent  in  an 
apivard  direction  when  the  wing  descends,  the  upward  bending 
of  the  elastic  feathers  contributing  to  the  horizontal  travel  of 
the  body  of  the  bird. 

I  have  been  careful  to  expound  Borelli's  views  for  several 
reasons  : — 

1st,  Because  the  purely  mechanical  theory  of  the  wing's 
action  is  clearly  to  be  traced  to  him. 

2d,  Because  his  doctrines  have  remained  unquestioned  for 
nearly  two  centuries,  and  have  been  adopted  by  all  the  writers 
since  his  time,  without,  I  regret  to  say  in  the  majority  of 
cases,  any  acknowledgment  whatever. 

3d,  Because  his  views  have  been  revived  by  the  modern 
French  school ;  and 

4th,  Because,  in  commenting  upon  and  differing  from 
Borelli,  I  will  necessarily  comment  upon  and  differ  from  all 
his  successors. 

As  to  the  Direction  of  the  Stroke,  yielding  of  the  Wing,  etc. — 
The  Duke  of  Argyll1  agrees  with  Borelli  in  believing  that  the 
wing  invariably  strikes  perpendicularly  downwards.  His  words 
are — "  Except  for  the  purpose  of  arresting  their  flight  birds 
can  never  strike  except  directly  downwards ;  that  is,  against 
the  opposing  force  of  gravity."  Professor  Owen  in  his  Com- 
parative Anatomy,  Mr.  Macgillivray  in  his  British  Birds,  Mr. 
Bishop  in  his  article  "  Motion  "  in  the  Cyclopedia  of  Anatomy 
f  "  Reign  of  Law"— Good  Words,  1865. 


AERONAUTICS.  225 

and  Physiology,  and  M.  Liais  "  On  the  Flight  of  Birds  and 
Insects  "  in  the  Annals  of  Natural  History,  all  assert  that  the 
stroke  is  delivered  downwards  and  more  or  less  backwards. 

To  obtain  an  upward  recoil,  one  would  naturally  suppose  all 
that  is  required  is  a  downward  stroke,  and  to  obtain  an  upward 
and  forward  recoil,  one  would  naturally  conclude  a  downward 
and  backward  stroke  alone  is  requisite.  Such,  however,  is  not 
the  case. 

In  the  first  place,  a  natural  wing,  or  a  properly  constructed 
artificial  one,  cannot  be  depressed  either  vertically  downwards, 
or  downwards  and  backwards.  It  will  of  necessity  descend 
downwards  and  forwards  in  a  curve.  This  arises  from  its 
being  flexible  and  elastic  throughout,  and  in  especial  from  its 
being  carefully  graduated  as  regards  thickness,  the  tip  being 
thinner  and  more  elastic  than  the  root,  and  the  posterior 
margin  than  the  anterior  margin. 

In  the  second  place,  there  is  only  one  direction  in  which 
the  wing  could  strike  so  at  once  to  support  and  carry  the  bird 
forward.  The  bird,  when  flying,  is  a  body  in  motion.  It  has 
therefore  acquired  momentum.  If  a  grouse  is  shot  on  the 
wing  it  does  not  fall  vertically  downwards,  as  Borelli  and  his 
successors  assume,  but  downwards  and  forwards.  The  flat 
surfaces  of  the  wings  are  consequently  made  to  strike  down- 
wards and  forwards,  as  they  in  this  manner  act  as  kites  to 
the  falling  body,  which  they  bear,  or  tend  to  bear,  upwards 
and  forwards. 

So  much  for  the  direction  of  the  stroke  during  the  descent 
of  the  wing. 

Let  us  now  consider  to  what  extent  the  posterior  margin 
of  the  wing  yields  in  an  upward  direction  when  the  wing 
descends.  Borelli  does  not  state  the  exact  amount.  The 
Duke  of  Argyll,  who  believes  with  Borelli  that  the  posterior 
margin  of  the  wing  is  elevated  during  the  down  stroke,  avers 
that,  "  whereas  the  air  compressed  in  the  hollow  of  the  wing 
cannot  pass  through  the  wing  owing  to  the  closing  upwards  of 
the  feathers  against  each  other,  or  escape  forwards  because  of 
the  rigidity  of  the  bones  and  of  the  quills  in  this  direction,  it 
passes  backwards,  and  in  so  doing  lifts  by  its  force  tlie  elastic 
ends  of  the  feathers.  In  passing  backwards  it  communicates 
11 


226  AERONAUTICS. 

to  the  whole  line  of  both  wings  a  corresponding  push  forwards 
to  the  body  of  the  bird.  The  same  volume  of  air  is  thus 
made,  in  accordance  with  the  law  of  action  and  reaction,  to 
sustain  the  bird  and  carry  it  forward."1  Mr.  Macgillivray 
observes  that  "  to  progress  in  a  horizontal  direction  it  is  neces- 
sary that  the  downward  stroke  should  be  modified  by  the  ele- 
vation in  a  certain  degree  of  the  free  extremities  of  the  quills."  2 

Marey's  Views. — Professor  Marey  states  that  during  the 
down  stroke  the  posterior  or  flexible  margin  of  the  wing  yields 
in  an  upward  direction  to  such  an  extent  as  to  cause  the  under 
surface  of  the  wing  to  look  backwards,  and  make  a  backward 
angle  with  the  horizon  of  45°  plus  or  minus  according  to 
circumstances.3  That  the  posterior  margin  of  the  wing  yields 
in  a  slightly  upward  direction  during  the  down  stroke,  I 
admit.  By  doing  so  it  prevents  shock,  confers  continuity  of 
motion,  and  contributes  in  some  measure  to  the  elevation  of 
the  wing.  The  amount  of  yielding,  however,  is  in  all  cases 
very  slight,  and  the  little  upward  movement  there  is,  is  in 
part  the  result  of  the  posterior  margin  of  the  wing  rotating 
around  the  anterior  margin  as  an  axis.  That  the  posterior 
margin  of  the  wing  never  yields  in  an  upward  direction  until 
the  under  surface  of  the  pinion  makes  a  backward  angle 
of  45°  with  the  horizon,  as  Marey  remarks,  is  a  matter  of 
absolute  certainty.  This  statement  admits  of  direct  proof. 
If  any  one  watches  the  horizontal  or  upward  flight  of  a  large 
bird,  he  will  observe  that  the  posterior  or  flexible  margin  of 
the  wing  never  rises  during  the  down  stroke  to  a  perceptible 
extent,  so  that  the  under  surface  of  the  wing  on  no  occasion 
looks  backwards,  as  stated  by  Marey.  On  the  contrary,  he 
will  find  that  the  under  surface  of  the  wing  (during  the  down 
stroke)  invariably  looks  forwards — the  posterior  margin  of 
the  wing  being  inclined  downwards  and  backwards;  as  shown 
at  figs.  82  and  83,  p.  158;  fig.  103,  p.  186;  fig.  85  (abc), 
p.  160;  and  fig.  88  (cdefg),  p.  1136. 

The  under  surface  of  the  wing,  as  will  be  seen  from  this 

1   "  Reign  of  Law"— Good  Words,  February  1865,  p.  128. 

*  History  of  British  Birds.     Lond.  1837,  p.  43. 

3  "  Mechanisnie  du  vol  chez  les  insectes.  Comment  se  fait  la  propulsion," 
by  Professor  E.  J.  Marey.  Revue  des  Cours  Scientifiques  de  la  France  et  de 
1'Etranger,  for  20th  March  1869,  p.  254. 


AERONAUTICS.  227 

account,  not  only  always  looks  forwards,  but  it  forms  a  true 
kite  with  the  horizon,  the  angles  made  by  the  kite  varying  at 
every  part  of  the  down  stroke,  as  shown  more  particularly  at 
d,  e>f>  9 ;  j)  &»  l> m  °f  %•  88,  p.  166.  I  am  therefore  opposed 
to  Borelli,  Macgillivray,  Owen,  Bishop,  M.  Liais,  the  Duke  of 
Argyll,  and  Marey  as  to  the  direction  and  nature  of  the  down 
stroke.  I  differ  also  as  to  the  direction  and  nature  of  the  up 
stroke. 

Professor  Marey  states  that  not  only  does  the  posterior 
margin  of  the  wing  yield  in  an  upward  •direction  during 
the  down  stroke  until  the  under  surface  of  the  pinion  makes 
a  backward  angle  of  45°  with  the  horizon,  but  that  during 
the  up  stroke  it  yields  to  the  same  extent  in  an  opposite  direc- 
tion. The  posterior  flexible  margin  of  the  wing,  according 
to  Marey,  passes  through  a  space  of  90°  every  time  the  wing 
reverses  its  course,  this  space  being  dedicated  to  the  mere 
adjusting  of  the  planes  of  the  wing  for  the  purposes  of 
flight.  The  planes,  moreover,  he  asserts,  are  adjusted  not  by 
vital  and  vito-mechanical  acts  but  by  the  action  of  the  air 
alone  ;  this  operating  on  the  under  surface  of  the  wing  and 
forcing  its  posterior  margin  upwards  during  the  down  stroke  ; 
the  air  during  the  up  stroke  acting  upon  the  posterior  margin 
of  the  upper  surface  of  the  wing,  and  forcing  it  downwards. 
This  is  a  mere  repetition  of  Borelli's  view.  Marey  dele- 
gates to  the  air  the  difficult  and  delicate  task  of  arranging 
the  details  of  flight.  The  time,  power,  and  space  occupied 
in  reversing  the  wing  alone,  according  to  this  theory,  are  such 
as  to  render  flight  impossible.  That  the  wing  does  not  act 
as  stated  by  Borelli,  Marey,  and  others  may  be  readily  proved 
by  experiment.  It  may  also  be  demonstrated  mathematically, 
as  a  reference  to  figs.  114  and  115,  p.  228,  will  show. 

Let  a  b  of  fig.  114  represent  the  horizon ;  m  n  the  line  of 
vibration ;  x  c  the  wing  inclined  at  an  upward  backward 
angle  of  45°  in  the  act  of  making  the  down  stroke,  and  x  d 
the  wing  inclined  at  a  downward  backward  angle  of  45°  and 
in  the  act  of  making  the  up  stroke.  When  the  wing  xc 
descends  it  will  tend  to  dive  downwards  in  the  direction  / 
giving  very  little  of  any  horizontal  support  (a  b)  j  when  the 
wing  x  d  ascends  it  will  endeavour  to  rise  in  the  direction  g,  as 
it  darts  up  like  a  kite  (the  body  bearing  it  being  in  motion). 


228 


AEKONAUTICS. 


If  we  take  the  resultant  of  these  two  forces,  we  have  at  most 
propulsion  in  the  direction  a  b.  This,  moreover,  would  only 
hold  true  if  the  bird  was  as  light  as  air.  As,  however,  gravity 
tends  to  pull  the  bird  downwards  as  it  advances,  the  real 
flight  of  the  bird,  according  to  this  theory,  would  fall  in 
a  line  between  b  and  /,  probably  in  x  h.  It  could  not  possibly 
be  otherwise ;  the  wing  described  and  figured  by  Borelli  and 
Marey  is  in  one  piece,  and  made  to  vibrate  vertically  on  either 
side  of  a  given  line.  If,  however,  a  wing  in  one  piece  is 
elevated  and  depressed  in  a  strictly  perpendicular  direction, 
it  is  evident  that  the  wing  will  experience  a  greater  resist- 
ance during  the  up  stroke,  when  it  is  acting  against  gravity, 
than  during  the  down  stroke,  when  it  is  acting  with  gravity. 


ft 


<l 


As  a  consequence,  the  bird  will  be  more  vigorously  depressed 
during  the  ascent  of  the  wing  than  it  will  be  elevated  during 
its  descent.  That  the  mechanical  wing  referred  to  by  Borelli 
and  Marey  is  not  a  flying  wing,  but  a  mere  propelling  ap- 
paratus, seems  evident  to  the  latter,  for  he  states  that  the 
winged  machine  designed  by  him  has  unquestionably  not 
motor  power  enough  to  support  its  own  weight}- 

The  manner  in  which  the  natural  wing  (and  the  artificial 
wing  properly  constructed  and  propelled)  evades  the  resistance 
of  the  air  during  the  up  stroke,  and  gives  continuous  support 
and  propulsion,  is  very  remarkable.  Fig.  115  illustrates  the 
true  principle.  Let  a  b  represent  the  horizon ;  m  n  the  direc- 
tion of  vibration;  xs  the  wing  ready  to  make  the  down 
stroke,  and  x  t  the  wing  ready  to  make  the  up  stroke.  When 
the  wing  xs  descends,  the  posterior  margin  (s)  is  screwed 

1  Revue  des  Cours  Scientifiques  de  la  France  et  de  1'Etranger.    8vo.    March 
20,  1869. 


AERONAUTICS.  229 

downwards  and  forwards  in  the  direction  s,  t;  the  forward  angle 
which  it  makes  with  the  horizon  increasing  as  the  wing 
descends  (compare  with  fig.  85  (a  be),  p.  160,  and  fig.  88 
(cdef),  p.  166).  The  air  is  thus  seized  by  a  great  variety 
of  inclined  surfaces,  and  as  the  under  surface  of  the  wing, 
which  is  a  true  kite,  looks  upwards  and  forwards,  it  tends  to 
carry  the  body  of  the  bird  upwards  and  forwards  in  the  direc- 
tion x  w.  When  the  wing  x  t  makes  the  up  stroke,  it  rotates 
in  the  direction  ts  to  prepare  for  the  second  down  stroke. 
It  does  not,  however,  ascend  in  the  direction  ts.  On  the 
contrary,  it  darts  up  like  a  true  kite,  which  it  is,  in  the  direc- 
tion x  v,  in  virtue  of  the  reaction  of  the  air,  and  because  the 
body  of  the  bird,  to  which  it  is  attached,  has  a  forward 
motion  communicated  to  it  by  the  wing  during  the  down 
stroke  (compare  with  ghi  of  fig.  88,  p.  166).  The  resultant 
of  the  forces  acting  in  the  directions  x  v  and  x  b,  is  one  acting  in 
the  direction  x  w,  and  if  allowance  be  made  for  the  operation 
of  gravity,  the  flight  of  the  bird  will  correspond  to  a  line 
somewhere  between  w  and  b,  probably  the  line  x  r.  This 
result  is  produced  by  the  wing  acting  as  an  eccentric — by 
the  upper  concave  surface  of  the  pinion  being  always  directed 
upwards,  the  under  concave  surface  downwards — by  the 
under  surface,  which  is  a  true  kite,  darting  forward  in  wave 
curves  both  during  the  down  and  up  strokes,  and  never 
making  a  backward  angle  with  the  horizon  (fig.  88,  p.  166); 
and  lastly,  by  the  wing  employing  the  air  under  it  as  a  ful- 
crum during  the  down  stroke,  the  air,  on  its  own  part,  react- 
ing on  the  under  surface  of  the  pinion,  and  when  the  proper 
time  arrives,  contributing  to  the  elevation  of  the  wing. 

If,  as  Borelli  and  his  successors  believe,  the  posterior 
margin  of  the  wing  yielded  to  a  marked  extent  in  an  upward 
direction  during  the  down  stroke,  and  more  especially  if  it 
yielded  to  such  an  extent  as  to  cause  the  under  surface  of  the 
wing  to  make  a  backward  angle  with  the  horizon  of  45°,  one  of 
two  things  would  inevitably  follow — either  the  air  on  which 
the  wing  depends  for  support  and  propulsion  would  be  per- 
mitted to  escape  before  it  was  utilized ;  or  the  wing  would 
dart  rapidly  downward,  and  carry  the  body  of  the  bird  with 
it.  If  the  posterior  margin  of  the  wing  yielded  in  an  upward 
direction  to  the  extent  described  by  Marey  during  the  down 


230  AERONAUTICS. 

stroke,  it  would  be  tantamount  to  removing  the  fulcrum  (the 
air)  on  which  the  lever  formed  by  the  wing  operates. 

If  a  bird  flies  in  a  horizontal  direction  the  angles  made  by 
the  under  surface  of  the  wing  with  the  horizon  are  very  slight, 
but  they  always  look  forwards  (fig.  60,  p.  126).  If  a  bird 
flies  upwards  the  angles  in  question  are  increased  (fig.  59,  p. 
126).  In  no  instance,  however,  unless  when  the  bird  is 
everted  and  flying  downwards,  is  the  posterior  margin  of  the 
wing  on  a  higher  level  than  the  anterior  one  (fig.  106,  p. 
203).  This  holds  true  of  natural  flight,  and  consequently 
also  of  artificial  flight. 

These  remarks  are  more  especially  applicable  to  the  flight 
of  the  bat  and  bird  where  the  wing  is  made  to  vibrate  more 
or  less  perpendicularly  (fig.  17,  p.  36;  figs.  82  and  83,  p. 
158.  Compare  with  fig.  85,  p.  160,  and  fig.  88,  p.  166).  If 
a  bird  or  a  bat  wishes  to  fly  upwards,  its  flying  surfaces 
must  always  be  inclined  upwards.  It  is  the  same  with  the 
fish.  A  fish  can  only  swim  upwards  if  its  body  is  directed 
upwards.  In  the  insect,  as  has  been  explained,  the  wing 
is  made  to  vibrate  in  a  more  or  less  horizontal  direction. 
In  this  case  the  wing  has  not  to  contend  directly  against 
gravity  (a  wing  which  flaps  vertically  must).  As  a  conse- 
quence it  is  made  to  tack  upon  the  air  obliquely  zigzag  fashion 
as  horse  and  carriage  would  ascend  a  steep  hill  (vide  figs.  67 
to  70,  p.  141.  Compare  with  figs.  71  and  72,  p.  144).  In 
this  arrangement  gravity  is  overcome  by  the  wing  reversing  its 
planes  and  acting  as  a  kite  which  flies  alternately  forwards  and 
backwards.  The  kites  formed  by  the  wings  of  the  bat  and  bird 
always  fly  forward  (fig.  88,  p.  166).  In  the  insect,  as  in  the  bat 
and  bird,  the  posterior  margin  of  the  wing  never  rises  above  the 
horizon  so  as  to  make  an  upward  and  backward  angle  with  it,  as 
stated  by  Borelli,  Marey,  and  others  (ex a  of  fig.  114,  p.  228). 

While  Borelli  and  his  successors  are  correct  as  to  the  wedge- 
action  of  the  wing,  they  have  given  an  erroneous  interpretation 
of  the  manner  in  which  the  wedge  is  produced.  Thus  Borelli 
states  that  when  the  wings  descend  their  posterior  margins 
ascend,  the  two  wings  forming  a  cone  whose  base  is  repre- 
sented by  cbe  of  fig.  113,  p.  220);  its  apex  being  repre- 
sented by  af  of  the  same  figure.  The  base  of  Borelli's  cone, 
it  will  be  observed,  is  inclined  forwards  in  the  direction  of 


AERONAUTICS. 


231 


the  head  of  the  bird.  Now  this  is  just  the  opposite  of  what 
ought  to  be.  Instead  of  the  two  wings  forming  one  cone, 
the  base  of  which  is  directed  forwards,  each  wing  of  itself 
forms  two  cones,  the  bases  of  which  are  directed  backwards 
and  outwards,  as  shown  at  fig.  116. 


Fm.  116. 

In  this  figure  the  action  of  the  wing  is  compared  to  the 
sculling  of  an  oar,  to  which  it  bears  a  considerable  resem- 
blance.1 The  one  cone,  viz.,  that  with  its  base  directed  out- 
wards, is  represented  at  x  b  d.  This  cone  corresponds  to  the 
area  mapped  out  by  the  tip  of  the  wing  in  the  process  of  elevat- 
ing. The  second  cone,  viz.,  that  with  its  base  directed  back- 
wards, is  represented  at  qp  n.  This  cone  corresponds  to  the  area 
mapped  out  by  the  posterior  margin  of  the  wing  in  the  process 
of  propelling.  The  two  cones  are  produced  in  virtue  of  the 
wing  rotating  on  its  root  and  along  its  anterior  margin  as  it 
ascends  and  descends  (fig.  80,  p.  149  ;  fig.  83,  p.  158).  The 
present  figure  (116)  shows  the  double  twisting  action  of  the 
wing,  the  tip  describing  the  figure-of-8  indicated  at  b  efy  //  d 
ijkl;  the  posterior  margin  describing  the  figure-of-8  indi- 
cated at  p  r  n.  It  is  in  this  manner  the  cross  pulsation  or  wave 
referred  to  at  p.  148  is  produced.  To  represent  the  action  of 
the  wing  the  sculling  oar  (ab,xs,cd)  must  have  a  small  scull 
(m  n,  q  r,  op)  working  at  right  angles  to  it.  This  follows  Ixv.-msr 

1  In  sculling  strictly  speaking,  it  is  the  upper  surface  of  (lie  oar  which  is 
most  effective  ;  whereas  in  Hying  it  is  the  under. 


232  AERONAUTICS. 

the  wing  has  to  elevate  as  well  as  propel ;  the  oar  of  a  boat 
when  employed  as  a  scull  only  propelling.  In  order  to  elevate 
more  effectually,  the  oars  formed  by  the  wings  are  made  to 
oscillate  on  a  level  with  and  under  the  volant  animal  rather 
than  above  it;  the  posterior  margins  of  the  wings  being  made 
to  oscillate '  on  a  level  with  and  below  the  anterior  margins 
(pp.  150,  151). 

Borelli,  and  all  who  have  written  since  his  time,  are 
unanimous  in  affirming  that  the  horizontal  transference  of  the 
body  of  the  bird  is  due  to  the  perpendicular  vibration  of  the 
wings,  and  to  the  yielding  of  the  posterior  or  flexible  margins 
of  the  wings  in  an  upward  direction  as  the  wings  descend. 
I  am,  however,  as  already  stated,  disposed  to  attribute 
the  transference,  1st,  to  the  fact  that  the  wings,  both  when 
elevated  and  depressed,  leap  forwards  in  curves,  those  curves 
uniting  to  form  a  continuous  waved  track;  2d,  to  the 
tendency  which  the  body  of  the  bird  has  to  swing  for- 
wards, in  a  more  or  less  horizontal  direction,  when  once  set 
in  motion;  3d,  to  the  construction  of  the  wings  (they  are 
elastic  helices  or  screws,  which  twist  and  untwist  when  they 
are  made  to  vibrate,  and  tend  to  bear  upwards  and  onwards 
any  weight  suspended  from  them) ;  4th,  to  the  reaction  of 
the  air  on  the  under  surfaces  of  the  wings,  which  always  act 
as  kites ;  5th,  to  the  ever-varying  power  with  which  the 
wings  are  urged,  this  being  greatest  at  the  beginning  of 
the  down  stroke,  and  least  at  the  end  of  the  up  one ;  6th, 
to  the  contraction  of  the  voluntary  muscles  and  elastic  liga- 
ments; 7th,  to  the  effect  produced  by  the  various  inclined 
surfaces  formed  by  the  wings  during  their  oscillations  ;  8th, 
to  the  weight  of  the  bird — weight  itself,  when  acting  upon 
inclined  planes  (wings),  becoming  a  propelling  power,  and  so 
contributing  to  horizontal  motion.  This  is  proved  by  the 
fact  that  if  a  sea  bird  launches  itself  from  a  cliff  with  ex- 
panded motionless  wings,  it  sails  along  for  an  incredible 
distance  before  it  reaches  the  water  (fig.  103,  p.  186). 

The  authors  who  have  adopted  Borelli's  plan  of  artificial 
wing,  and  who  have  indorsed  his  mechanical  views  of  the 
action  of  the  wing  most  fully,  are  Chabrier,  Straus-Durckheim, 
Girard,  and  Marey.  Borelli's  artificial  wing,  as  already  ex- 
plained (p.  220,  fig.  113),  consists  of  a  rigid  rod  (e,r)  in 


AERONAUTICS.  233 

front,  and  a  flexible  sail  (a,  o)  composed  of  feathers,  behind.  It 
acts  upon  the  air,  and  the  air  acts  upon  it,  as  occasion  demands. 

Chabrier's  Views. — Chabrier  states  that  the  wing  has  only 
one  period  of  activity — that,  in  fact,  if  the  wing  be  suddenly 
lowered  by  the  depressor  muscles,  it  is  elevated  solely  by  the 
reaction  of  the  air.  There  is  one  unanswerable  objection  to 
this  theory — the  bats  and  birds,  and  some,  if  not  all  the 
insects,  have  distinct  elevator  muscles.  The  presence  of  well- 
developed  elevator  muscles  implies  an  elevating  function,  and, 
besides,  we  know  that  the  insect,  bat,  and  bird  can  elevate 
their  wings  when  they  are  not  flying,  and  when,  consequently, 
no  reaction  of  the  air  is  induced. 

Straus- Durckheim' s  Views. — Durckheim  believes  the  insect 
abstracts  from  the  air  by  means  of  the  inclined  plane  a  com- 
ponent force  (composant)  which  it  employs  to  support  and 
direct  itself.  In  his  Theology  of  Nature  he  describes  a  sche- 
matic wing  as  follows  : — It  consists  of  a  rigid  ribbing  in  front, 
and  a  flexible  sail  behind.  A  membrane  so  constructed  will, 
according  to  him,  be  fit  for  flight.  It  will  suffice  if  such  a 
sail  elevates  and  lowers  itself  successively.  It  will,  of  its  own 
accord,  dispose  itself  as  an  inclined  plane,  and  receiving 
obliquely  the  reaction  of  the  air,  it  transfers  into  tractile  force  a 
part  of  the  vertical  impulsion  it  has  received.  These  two  parts 
of  the  wing  are,  moreover,  equally  indispensable  to  each  other. 
If  we  compare  the  schematic  wing  of  Durckheim  with  that  of 
Borelli  they  will  be  found  to  be  identical,  both  as  regards 
their  construction  and  the  manner  of  their  application. 

Professor  Marey,  so  late  as  1869,  repeats  the  arguments 
and  views  of  Borelli  and  Durckheim,  with  very  trifling  altera- 
tions. Marey  describes  two  artificial  wings,  the  one  composed 
of  a  rigid  rod  and  sail — the  rod  representing  the  stiff  anterior 
margin  of  the  wing ;  the  sail,  which  is  made  of  paper  bordered 
with  card-board,  the  flexible  posterior  portion.  The  other 
wing  consists  of  a  rigid  nervure  in  front  and  behind  of  thin 
parchment  Tjjhich  supports  fine  rods  of  steel.  He  states,  that 
if  the  wing  only  elevates  and  depresses  itself,  "  the  resistance 
of  the  air  is  sufficient  to  produce  all  the  other  movements. 
In  effect  the  wing  pf  an  insect  has  not  the  power  of  equal 
resistance  in  every  part.  On  the  anterior  margin  the  extended 
nervures  make  it  rigid,  while  behind  it  is  fine  and  flexible,. 


234  AERONAUTICS. 

During  the  vigorous  depression  of  the  wing  the  nervure  has 
the  power  of  remaining  rigid,  whereas  the  flexible  portion, 
being  pushed  in  an  upward  direction  on  account  of  the  resist- 
ance it  experiences  from  the  air,  assumes  an  oblique  position, 
which  causes  the  upper  surface  of  the  wing  to  look  fwwards." 
..."  At  first  the  plane  of  the  wing  is  parallel  with  the  body 
of  the  animal.  It  lowers  itself — the  front  part  of  the  wing 
strongly  resists,  the  sail  which  follows  it  being  flexible  yields. 
Carried  by  the  ribbing  (the  anterior  margin  of  the  wing)  which 
lowers  itself,  the  sail  or  posterior  margin  of  the  wing  being 
raised  meanwhile  by  the  air,  which  sets  it  straight  again, 
the  sail  will  take  an  intermediate  position,  and  incline  itself 
about  45°  plus  or  minus  according  to  circumstances.  The 
wing  continues  its  movements  of  depression  inclined  to  the  hori- 
zon, but  the  impulse  of  the  air  which  continues  its  effect,  and 
naturally  acts  upon  the  surface  which  it  strikes,  has  the  power 
of  resolving  itself  into  two  forces,  a  vertical  and  a  Jwrizontal 
force,  the  first  suffices  to  raise  the  animal,  the  second  to  move 
it  along."  x  The  reverse  of  this,  Marey  states,  takes  place  during 
the  elevation  of  the  wing — the  resistance  of  the  air  from  above 
causing  the  upper  surface  of  the  wing  to  look  backwards.  The 
fallaciousness  of  this  reasoning  has  been  already  pointed 

1  Compare  Marey's  description  with  that  of  Borelli,  a  translation  of  which 
I  subjoin.  "  Let  a  bird  be  suspended  in  the  air  with  its  wings  expanded, 
and  first  let  the  nnder  surfaces  (of  the  wings)  be  struck  by  the  air"  ascending 
perpendicularly  to  the  horizon  with  such  a  force  that  the  bird  gliding  down 
is  prevented  from  falling :  I  say  that  it  (the  bird)  will  be  impelled  with  a 
horizontal  forward  motion,  because  the  two  osseous  rods  of  the  wings  are 
able,  owing  to  the  strength  of  the  muscles,  and  because  of  their  hardness,  to 
resist  the  force  of  the  air,  and  therefore  to  retain  the  same  form  (literally  ex- 
tent, expansion),  but  the  total  breadth  of  the  fan  of  each  wing  yields  to  the 
impulse  of  the  air  when  the  flexible  feathers  are  permitted  to  rotate  around 
the  manubrifi  or  osseous  axes,  and  hence  it  is  necessary  that  the  extremities 
of  the  wings  approximate  each  other  :  wherefore  the  wings  acquire  the  form 
of  a  wedge  whose  point  is  directed  towards  the  tail  of  the  bird,  but  whose 
surfaces  are  compressed  on  either  side  by  the  ascending  air  in  such  a  manner 
that  it  is  driven  out  in  the  direction  of  its  base.  Since,  however,  the  wedge 
formed  by  the  wings  cannot  move  forward  unless  it  carry  the  body  of  the  bird 
along  with  it,  it  is  evident  that  it  (the  wedge)  gives  place  to  the  air  impelling 
it,  and  therefore  the  bird  flies  forward  in  a  horizontal  direction.  But  now  let 
the  substratum  of  still  air  be  struck  by  the  fans  (feathers)  of  the  wings  with 
a  motion  perpendicular  to  the  horizon.  Since  the  fans  and  sails  of  the  wings 


AERONAUTICS.  235 

out,  and  need  not  be  again  referred  to.  It  is  not  a  little 
curious  that  Borelli's  artificial  wing  should  have  been 
reproduced  in  its  integrity  at  a  distance  of  nearly  two 
centuries. 

The  AutJwr's  Views: — his  Mcilwd  of  constructing  and  applying 
Artificial  Wings  as  contra-distinguished  from  that  of  Borelli, 
Chabrier,  Durckheim,  Marey,  etc. — The  artificial  wings  which  I 
have  been  in  the  habit  of  making  for  several  years  differ  from 
those  recommended  by  Borelli,  Durckheim,  and  Marey  in 
four  essential  points  : — 

1st,  The  mode  of  construction. 

2d,  The  manner  in  which  they  are  applied  to  the  air. 

3d,  The  nature  of  the  power  employed. 

4:th,  The  necessity  for  adapting  certain  elastic  substances 
to  the  root  of  the  wing  if  in  one  piece,  and  to  the  root  and 
the  body  of  the  wing  if  in  several  pieces. 

And,  first,  as  to  the  manner  of  construction. 

Borelli,  Durckheim,  and  Marey  maintain  that  the  anterior 
margin  of  the  wing  should  be  rigid ;  I,  on  the  other  hand, 
believe  that  no  part  of  the  wing  whatever  should  be  rigid, 
not  even  the  anterior  margin,  and  that  the  pinion  should  be 
flexible  and  elastic  throughout. 

That  the  anterior  margin  of  the  wing  should  not  be  com- 
posed of  a  rigid  rod  may,  I  think,  be  demonstrated  in  a 
variety  of  ways.  If  a  rigid  rod  be  made  to  vibrate  by  the 
hand  the  vibration  is  not  smooth  and  continuous ;  on  the 
contrary,  it  is  irregular  and  jerky,  and  characterized  by  two 
halts  or  pauses  (dead  points),  the  one  occurring  at  the  end  of 
the  up  stroke,  the  other  at  the  end  of  the  down  stroke.  This 
mechanical  impediment  is  followed  by  serious  consequences 
as  far  as  power  and  speed  are  concerned — the  slowing  of  the 
wing  at  the  end  of  the  down  and  up  strokes  involving  a 

acquire  the  form  of  a  wedge,  the  point  of  which  is  turned  towards  the  tail 
(of  the  bird),  and  since  they  suffer  the  same  force  and  compression  from 
the  air,  whether  the  vibrating  wings  strike  the  undisturbed  air  beneath,  or 
whether,  on  the  other  hand,  the  expanded  wings  (the  osseous  axes  remain- 
ing rigid)  receive  the  percussion  of  the  ascending  air ;  in  either  case  the 
flexible  /fathers  yield  to  the  impulse,  and  hence  approximate  each  other,  and 
thus  the  bird  moves  in  a  forward  direction.'1'1 — De  Motu  Animalium,  pars 
prima,  prop.  196,  1685. 


236  AERONAUTICS. 

great  expenditure  of  power  and  a  disastrous  waste  of  time. 
The  wing,  to  be  effective  as  an  elevating  and  propelling 
organ,  should  have  no  dead  points,  and  should  be  character- 
ized by  a  rapid  winnowing  or  fanning  motion.  It  should 
reverse  and  reciprocate  with  the  utmost  steadiness  and 
smoothness — in  fact,  the  motions  should  appear  as  continuous 
as  those  of  a  fly-wheel  in  rapid  motion :  they  are  so  in  the 
insect  (figs.  64,  65,  and  66,  p.  139). 

To  obviate  the  difficulty  in  question,  it  is  necessary,  in  my 
opinion,  to  employ  a,  tapering  elastic  rod  or  series  of  rods 
bound  together  for  the  anterior  margin  of  the  wing. 

If  a  longitudinal  section  of  bamboo  cane,  ten  feet  in  length, 
and  one  inch  in  breadth  (fig.  117),  be  taken  by  the  ex- 
tremity and  made  to  vibrate,  it  will  be  found  that  a  wavy 
serpentine  motion  is  produced,  the  waves  being  greatest 
when  the  vibration  is  slowest  (fig.  118),  and  least  when  it 
is  most  rapid  (fig.  119).  It  will  further  be  found  that  at 
the  extremity  of  the  cane  where  the  impulse  is  communi- 
cated there  is  a  steady  reciprocating  movement  devoid  of  dead 
points.  The  continuous  movement  in  question  is  no  doubt 
due  to  the  fact  that  the  different  portions  of  the  cane 
reverse  at  different  periods — the  undulations  induced  being 
to  an  interrupted  or  vibratory  movement  very  much  what 
the  continuous  play  of  a  fly-wheel  is  to  a  rotatory  motion. 

The  Wave  Wing  of  the  Autlior. — If  a  similar  cane  has  added 
to  it,  tapering  rods  of  whalebone,  which  radiate  in  an  out- 
ward direction  to  the  extent  of  a  foot  or  so,  and  the  whale- 
bones be  covered  by  a  thin  sheet  of  india-rubber,  an  artificial 
wing,  resembling  the  natural  one  in  all  its  essential  points, 
is  at  once  produced  (fig.  120).  I  propose  to  designate  this 
wing,  from  the  peculiarities  of  its  movements,  the  wave 
icing  (fig.  121).  If  the  wing  referred  to  (fig.  121)  be  made 
f.i  i  vibrate  at  its  root,  a  series  of  longitudinal  (c  d  e)  and 
rransverse  (/ ' g  Ti)  waves  are  at  once  produced;  the  one  series 
running  in  the  direction  of  the  length  of  the  wing,  the  other  in 
the  direction  of  its  breadth  (vide  p.  148).  This  wing  further 
deists  and  untwists,  figure-of-8  fashion,  during  the  up  and  down 
strokes,  as  shown  at  fig.  122,  p.  239  (compare  with  figs.  82 
and  83,  p.  158;  fig.  86,  p.  161;  and  fig.  103,  p.  186). 


AERONAUTICS. 


237 


There   is    moreover,  a   continuous  play  of  the   wing;  the 
down  stroke  gliding  into  the  up  one,  and  vice  versa, which 


FIG. 
117. 


FIG.  117.— Represents  a  longitudinal  section  of  bamboo  cane  ten  feet  long,  and 
one  inch  wide. — Original. 

FIG.  118.— The  appearance  presented  by  the  same  cane  when  made  to  vibrate 
by  the  hand.  The  cane  vibrates  on  either  side  of  a  given  line  (te  «),  and  ap- 
pears as  if  it  were  in  two  places  at  the  same  time,  viz.,  c  and  /,  g  and  d,  e  and 
A.  It  is  thus  during  its  vibration  thrown  into  figures-of-8  or  opposite  curves. 
—  Original 

FIG.  119.— The  same  cane  when  made  to  vibrate  more  rapidly.  In  this  case  the 
waves  made  by  the  cane  are  less  in  size,  but  more  numerous.  The  cane  is  seen 
alternately  on  either  side  of  the  line  x  ar,  being  now  at  *  now  at  »i,  now  at  » 
now  at,?,  now  at  k  now  at  o,  now  at  p  now  at  I.  The  cane,  when  made  to  vi- 
brate, has  no  dead  points,  a  circumstance  due  to  the  fact  that  no  two  parts  of 
It  reverse  or  change  their  curves  at  precisely  the  same  instant.  This  curious 
reciprocating  motion  enables  the  wing  to  seize  and  disengage  itself  from  the 
air  with  astonishing  rapidity. —  Original. 

FIG.  120.— The  same  cane  with  a  flexible  elastic  curtain  or  fringe  added  to  it.  The 
curtain  consists  of  tapering  whalebone  rods  covered  with  a  thin  layer  of  india- 
rubber,  a  b  anterior  margin  of  wing,  c  d  posterior  ditto. — Original. 

FIG.  121. — Gives  the  appearance  presented  by  the  artificial  wing  (fig.  120)  when 
made  to  vibrate  by  the  hand.  It  is  thrown  into  longitudinal  and  transverse 
waves.  The  longitudinal  waves  are  represented  by  the  arrows  c  d  e,  and 
the  transverse  waves  by  the  arrows  /  g  h.  A  wing  constructed  on  this 
principle  gives  a  continuous  elevating  and  propelling  power.  It  devetopes 
flgure-of-8  curves  during  its  action  in  longitudinal,  transverse,  and  oblique  di- 
rections. It  literally  floats  upon  the  air.  It  has  no  dead  points — is  vibrated 
with  amazingly  little  power,  and  has  apparently  no  slip.  It  can  fly  in  an  up- 
ward, downwa'rd,  or  horizontal  direction  by  merely  altering  its  angle  of  in- 
clination to  the  horizon.  It  is  applied  to  the  air  by  an  irregular  motion — the 
movement  being  most  sudden  and  vigorous  always  at  the  beginning  of  the 
down  stroke. — Original. 


238  AERONAUTICS. 

clearly  shows  that  the  down  and  up  strokes  are  parts  of  one 
whole,  and  that  neither  is  perfect  without  the  other. 

The  wave  wing  is  endowed  with  the  very  remarkable  pro- 
perty that  it  will  fly  in  any  direction,  demonstrating  more  or 
less  clearly  that  flight  is  essentially  a  progressive  movement, 
i.e.  a  horizontal  rather  than  a  vertical  movement.  Thus,  if 
the  anterior  or  thick  margin  of  the  wing  be  directed  up- 
wards, so  that  the  under  surface  of  the  wing  makes  a  forward 
-angle  with  the  horizon  of  45°,  the  wing  will,  when  made  to 
vibrate  by  the  hand,  fly  with  an  undulating  motion  in  an 
upward  direction,  like  a  pigeon  to  its  dovecot.  If  the  under 
surface  of  the  wing  makes  no  angle,  or  a  very  small  forward 
angle,  with  the  horizon,  it  will  dart  forward  in  a  series  of 
curves  in  a  horizontal  direction,  like  a  crow  in  rapid  horizontal 
flight.  If  the  anterior  or  thick  margin  of  the  wing  be  directed 
downwards,  so  that  the  under  surface  of  the  wing  makes  a 
backward  angle  of  45°  with  the  horizon,  the  wing  will  de- 
scribe a  waved  track,  and  fly  downwards,  as  a  sparrow  from 
a  house-top  or  from  a  tree  (p.  230).  In  all  those  move- 
ments progression  is  a  necessity.  The  movements  are 
continuous  gliding  forward  movements.  There  is  no  halt  or 
pause  between  the  strokes,  and  if  the  angle  which  the  under 
surface  of  the  wing  makes  with  the  horizon  be  properly 
regulated,  the  amount  of  steady  tractile  and  buoying  power 
developed  is  truly  astonishing.  This  form  of  wing,  which 
may  be  regarded  as  the  realization  of  the  figure-of-8  theory 
of  flight,  elevates  and  propels  both  during  the  down  and  up 
strokes,  and  its  working  is  accompanied  with  almost  no  slip. 
It  seems  literally  to  float  upon  the  air.  No  wing  that  is 
rigid  in  the  anterior  margin  can  twist  and  untwist  during  its 
action,  and  produce  the  figure-of-8  curves  generated  by  the 
living  wing.  To  produce  the  curves  in  question,  the  wing 
must  be  flexible,  elastic,  and  capable  of  change  of  form  in  all 
its  parts.  The  curves  made  by  the  artificial  wing,  as  has 
been  stated,  are  largest  when  the  vibration  is  slow,  and  least 
when  it  is  quick.  In  like  manner,  the  air  is  thrown  into 
large  waves  by  the  slow  movement  of  a  large  wing,  and  into 
small  waves  by  the  rapid  movement  of  a  smaller  wing.  The 
size  of  the  wing  curves  and  air  waves  bear  a  fixed  relation  to 
each  other,  and  both  are  dependent  on  the  rapidity  with 


AERONAUTICS. 


239 


which  the  wing  is  made  to  vibrate.  This  is  proved  by  the 
fact  that  insects,  in  order  to  fly,  require,  as  a  rule,  to  drive 
their  small  wings  with  immense  velocity.  It  is  further 
proved  by  the  fact  that  the  small  humming-bird,  in  order  to 
keep  itself  stationary  before  a  flower,  requires  to  oscillate  its 
tiny  wings  with  great  rapidity,  whereas  the  large  humming- 
bird (Patagona  gigas),  as  was  pointed  out  by  Darwin,  can 
attain  the  same  object  by  flapping  its  large  wings  with  a  very 
slow  and  powerful  movement.  In  the  larger  birds  the  move- 
ments are  slowed  in  proportion  to  the  -size,  and  more 
especially  in  proportion  to  the  length  of  the  wing ;  the  cranes 
and  vultures  moving  the  wings  very  leisurely,  and  the  large 
oceanic  birds  dispensing  in  a  great  measure  with  the  flapping 
of  the  wings,  and  trusting  for  progression  and  support  to  the 
wings  in  the  expanded  position. 


Fm.  122. 

FIG.  122. — Elastic  spiral  wing,  which  twists  and  untwists  during  its  action,  to 
form  a  mobile  helix  or  screw.  This  wing  is  made  to  vibrate  by  steam  by  a 
direct  piston  action,  and  by  a  slight  adjustment  can  be  propelled  vertically, 
horizontally,  or  at  any  degree  of  obliquity. 

a,  b.  Anterior  margin  of  wing,  to  which  the  neurse  or  ribs  are  affixed,    c,  d.  Pos- 
terior margin  of  wing  crossing  anterior  one.   x,  Ball-and-socket  joint  at  root  of 
wing  :  the  wing  being  attached  to  the  side  of  the  cylinder  by  the  socket.     /. 
Cylinder,     r,  r.  Piston,  with  cross  heads  (w,w)  and   piston  head  (*).     0,0, 
Stuffing  boxes.    e,f,  Driving  chains,    m,  Superior  elastic  band,  which  assists  in 
elevating  the  wing,     n,  Inferior  elastic  band,  which  antMOnisei  in.    Die  alter- 
nate stretching  of  the  superior  and  inferior  elastic  bands  contributes  1 
continuous  play  of  the  wing,  by  preventing  dead  points  at  the  end  of  the  down 
and  up  strokes.     The  wing  is  free  to  move  in  a  vertical  and  horizontal  d 
tionand  at  any  degree-of  obliquity.—  Original. 

This  leads  me  to  conclude  that  very  large  wings  may  be 
driven  with  a  comparatively  slow  motion,  a  matter  of  great 
importance  in  artificial  flight  secured  by  the  flapping  of 

wings. 


240  AERONAUTICS. 

How  to  construct  an  artificial  Wave  Wing  on  tJie  Insect 
type. — The  following  appear  to  me  to  be  essential  features  in 
the  construction  of  an  artificial  wing : — 

The  wing  should  be  of  a  generally  triangular  shape. 

It  should  taper  from  the  root  towards  the  tip,  and  from 
the  anterior  margin  in  the  direction  of  the  posterior  margin. 

It  should  be  convex  above  and  concave  below,  and  slightly 
twisted  upon  itself. 

It  should  be  flexible  and  elastic  throughout,  and  should 
twist  and  untwist  during  its  vibration,  to  produce  figure-of-8 
curves  along  its  margins  and  throughout  its  substance. 

Such  a  wing  is  represented  at  fig.  122,  p.  239. 

If  the  wing  is  in  more  than  one  piece,  joints  and  springs 
require  to  be  added  to  the  body  of  the  pinion. 

In  making  a  wing  in  one  piece  on  the  model  of  the  insect 
wing,  such  as  that  shown  at  fig.  122  (p.  239),  I  employ  one  or 
more  tapering  elastic  reeds,  which  arch  from  above  downwards 
(a  b)  for  the  anterior  margin.  To  this  I  add  tapering  elastic 
reeds,  which  radiate  towards  the  tip  of  the  wing,  and  which 
also  arch  from  above  downwards  (g,  h,  i}.  These  latter  are  so 
arranged  that  they  confer  a  certain  amount  of  spirality  upon 
the  wing ;  the  anterior  (a  &)  and  posterior  (c  d)  margins  being 
arranged  in  different  planes,  so  that  they  appear  to  cross  each 
other.  I  then  add  the  covering  of  the  wing,  which  may  con- 
sist of  india-rubber,  silk,  tracing  cloth,  linen,  or  any  similar 
substance. 

If  the  wing  is  large,  I  employ  steel  tubes,  bent  to  the 
proper  shape.  In  some  cases  I  secure  additional  strength  by 
adding  to  the  oblique  ribs  or  stays  (ghi  of  fig.  122)  a  series 
of  very  oblique  stays,  and  another  series  of  cross  stays,  as 
shown  at  m  and  a,  n,  o,p,  q  of  fig.  123,  p.  241. 

This  form  of  wing  is  made  to  oscillate  upon  two  centres 
viz.  the  root  and  anterior  margin,  to  bring  out  the  peculiar 
eccentric  action  of  the  pinion. 

If  I  wish  to  produce  a  very  delicate  light  wing,  I  do  so  by 
selecting  a  fine  tapering  elastic  reed,  as  represented  at  a  b  of 
fig.  124. 

To  this  I  add  successive  layers  (i,  h,  g,  f,  e)  of  some  flexible 
material,  such  as  parchment,  buckram,  tracing  cloth,  or  even 


AERONAUTICS. 


241 


paper.  As  the  layers  overlap  each  other,  it  follows  that  there 
are  five  layers  at  the  anterior  margin  (a  6),  and  only  one  at 
the  posterior  (cd).  This  form  of  wing  is  not  twisted  upon 
itself  structurally,  but  it  twists  and  untwists,  and  becomes  a 
true  screw  during  its  action. 


FIG.  123.—  Artificial  Wing  with  Perpendicular  (r  s)  and  Horizontal  (tu)  Elastic 
Bands  attached  to  ferrule  {w). 

a,  b,  Strong  elastic  reed,  which  tapers  towards  the  tip  of  the  wing. 

d,e,f,h,i,j,k,  Tapering  curved  reeds,  which  rim  obliquely  from  the 
anterior  to  the  posterior  margin  of  the  wing,  and  which  ladiutc  towards  the 
tip. 

m,  Similar  curved  reeds,  which  run  still  more  obliquely. 

a,  n,  o,  p,  q.  Tapering  curved  reeds,  which  run  from  the  anterior  margin  of 
the  wing,  and  at  right  angles  to  it.  Thes-j  support  the  two  sets  of  oblique 
reeds,  and  give  additional  strength  to  the  anterior  margin. 

x.  Ball-and-socket  joint,  by  which  the  root  of  the  wing  is  attached  to  the 
cylinder,  as  in  fig.  122,  p.  239.  —  Originul. 

FK;.  124. —Flexible  elastic  wing  with  tapering  elastic  reed  (aft)  running  along 
anterior  margin. 

c,  d,  Posterior  margin  of  wing  f,  Portion  of  wing  composed  of  our  layer 
of  flexible  material,  h.  Portion  of  wing  com  posed  of  two  layers,  g,  Portion 
of  wing  composed  of  three  layers  /,  Portion  of  wing  composed  of  four 
layers,  e.  Portion  of  wing  composed  of  five  layers,  x,  Ball-and-socket  joint 
at  root  of  wing. — Original. 

Fio.  125.— Flexible  valvular  wing  with  india-rubber  springs  attached  to  its 
root. 

a,  b.  Anterior  marpin  of  wing,  tapering  and  elastic,  c,  rf,  Posterior  margin 
of  wing,  elastic.  /,/./,  Segments  which  open  during  the  up  stroke  and 
close  during  the  down,  after  the  manner  of  valves.  These  are  very  narrow, 
and  open  and  close  instantly,  x,  Universal  joint,  m,  Superior  clastic 
band.  n,  Ditto  inferior,  o,  Ditto  anterior,  p,  q.  Ditto  oblique,  r,  l!ing 
into  which  the  clastic  bands  are  fixed. — Original. 

How  to  construct  a  Wave  Wing  which  shall  evade  tlie  suj>i-r- 
imposed  Air  during  tlie  Up  Stroke. — To  construct  a  wing  which 


242  AERONAUTICS. 

shall  elude  the  air  during  the  up  stroke,  it  is  necessary  to 
make  it  valvular,  as  shown  at  fig.  125,  p.  241. 

This  wing,  as  the  figure  indicates,  is  composed  of  numerous 
narrow  segments  (///),  so  arranged  that  the  air,  when  the 
wing  is  made  to  vibrate,  opens  or  separates  them  at  the 
beginning  of  the  up  stroke,  and  closes  or  brings  them  together 
at  the  beginning  of  the  down  stroke. 

The  time  and  power  required  for  opening  and  closing  the 
segments  is  comparatively  trifling,  owing  to  their  extreme 
narrowness  and  extreme  lightness.  The  space,  moreover, 
through  which  they  pass  in  performing  their  valvular  action 
is  exceedingly  small.  The  wing  under  observation  is  flexible 
and  elastic  throughout,  and  resembles  in  its  general  features 
the  other  wings  described. 

I  have  also  constructed  a  wing  which  is  self-acting  in 
another  sense.  This  consists  of  two  parts — the  one  part 
being  made  of  an  elastic  reed,  which  tapers  towards  the  ex- 
tremity ;  the  other  of  a  flexible  sail.  To  the  reed,  which 
corresponds  to  the  anterior  margin  of  the  wing,  delicate 
tapering  reeds  are  fixed  at  right  angles ;  the  principal  and 
subordinate  reeds  being  arranged  on  the  same  plane.  The 
flexible  sail  is  attached  to  the  under  surface  of  the  principal 
reed,  and  is  stiffer  at  its  insertion  than  towards  its  free  mar- 
gin. When  the  wing  is  made  to  ascend,  the  sail,  because  of 
the  pressure  exercised  upon  its  upper  surface  by  the  air, 
assumes  a  very  oblique  position,  so  that  the  resistance  ex- 
perienced by  it  during  the  up  stroke  is  very  slight.  When, 
however,  the  wing  descends,  the  sail  instantly  flaps  in  an 
upward  direction,  the  subordinate  reeds  never  permitting  its 
posterior  or  free  margin  to  rise  above  its  anterior  or  fixed 
margin.  The  under  surface  of  the  wing  consequently  descends 
in  such  a  manner  as  to  present  a  nearly  flat  surface  to  the  earth. 
It  experiences  much  resistance  from  the  air  during  the  down 
•  stroke,  the  amount  of  buoyancy  thus  furnished  being  very 
considerable.  The  above  form  of  wing  is  more  effective 
during  the  down  stroke  than  during  the  up  one.  It,  however, 
elevates  and  propels  during  both,  the  forward  travel  being 
greatest  during  the  down  stroke. 

Compound  Wave  Wing  of  the  Author. — In  order  to  render 


AERONAUTICS. 


243 


the  movements  of  the  wing  as  simple  as  possible,  I  was 
induced  to  devise  a  form  of  pinion,  which  for  the  sake  of  dis- 
tinction I  shall  designate  the  Compound  Wave  Wing.  This 
wing  consists  of  two  wave  wings  united  at  the  roots,  as 
represented  at  fig.  126.  It  is  impelled  by  steam,  its  centre 


being  fixed  to  the  head  of  the  piston  by  a  compound  joint 
(#),  which  enables  it  to  move  in  a  circle,  and  to  rotate  along  its 
anterior  margin  (a  b  c  d;  A,  A')  in  the  direction  of  its  length. 
The  circular  motion  is  for  steering  purposes  only.  The  wing 
rises  and  falls  with  every  stroke  of  the  piston,  and  the  move- 
ments of  the  piston  are  quickened  during  the  down  stroke, 
and  slowed  during  the  up  one. 

During  the  up  stroke  of  the  piston  the  wing  is  very 
decidedly  convex  on  its  upper  surface  (abed;  A, A'),  its 
under  surface  being  deeply  concave  and  inclined  obliquely 
upwards  and  forwards.  It  thus  evades  the  air  during  the  up 
stroke.  During  the  down  stroke  of  the  piston  the  wing  is 
flattened  out  in  every  direction,  and  its  extremities  twisted 
in  such  a  manner  as  to  form  two  screws,  as  shown  at  a'  V  c  d'; 
e'f'g'h';  £>,J?  of  figure.  The  active  area  of  the  wing  is  by 
this  means  augmented,  the  wing  seizing  the  air  with  givut 
avidity  during  the  down  stroke.  The  area  of  the  wing  may 
be  still  further  increased  and  diminished  (luring  the  down 
and  up  strokes  by  adding  joints  to  the  body  of  the  wing. 


244  AERONAUTICS. 

The  degree  of  convexity  given  to  the  upper  surface  of  the 
wing  can  be  increased  or  diminished  at  pleasure  by  causing  a 
cord  (ij;  A,  A')  and  elastic  band  (k)  to  extend  between  two 
points,  which  may  vary  according  to  circumstances.  The 
wing  is  supplied  with  vertical  springs,  which  assist  in  slowing 
and  reversing  it  towards  the  end  of  the  down  and  up  strokes, 
and  these,  in  conjunction  with  the  elastic  properties  of  the 
wing  itself,  contribute  powerfully  to  its  continued  play.  The 
compound  wave  wing  produces  the  currents  on  which  it 
rises.  Thus  during  the  up  stroke  it  draws  after  it  a  current, 
which  being  met  by  the  wing  during  its  descent,  confers 
additional  elevating  and  propelling  power.  During  the  down 
stroke  the  wing  in  like  manner  draws  after  it  a  current  which 
forms  an  eddy,  and  on  this  eddy  the  wing  rises,  as  explained 
at  p.  253,  fig.  129.  The  ascent  of  the  wing  is  favoured  by 
the  superimposed  air  playing  on  the  upper  surface  of  the 
posterior  margin  of  the  organ,  in  such  a  manner  as  to  cause 
the  wing  to  assume  a  more  and  more  oblique  position  with 
reference  to  the  horizon.  This  change  in  the  plane  of  the 
wing  enables  its  upper  surface  to  avoid  the  superincumbent 
air  during  the  up  stroke,  while  it  confers  upon  its  under  sur- 
face a  combined  kite  and  parachute  action.  The  compound 
wave  wing  leaps  forward  in  a  curve  both  during  the  down 
and  up  strokes,  so  that  the  wing  during  its  vibration  describes 
a  waved  track,  as  shown  at  a,  c,  e,g,  i  of  fig.  81,  p.  157.  The 
compound  wave  wing  possesses  most  of  the  peculiarities  of 
single  wings  when  made  to  vibrate  separately.  It  forms  a 
most  admirable  elevator  and  propeller,  and  has  this  advan- 
tage over  ordinary  wings,  that  it  can  be  worked  without 
injury  to  itself,  when  the  machine  which  it  is  intended  to 
elevate  is  resting  on  the  ground.  Two  or  more  compound 
wave  wings  may  be  arranged  on  the  same  plane,  or  super- 
imposed, and  made  to  act  in  concert.  They  may  also  by  a 
slight  modification  be  made  to  act  horizontally  instead  of 
vertically.  The  length  of  the  stroke  of  the  compound  wave 
wing  is  determined  in  part,  though  not  entirely  by  the  stroke 
of  the  piston — the  extremities  of  the  wing,  because  of  their 
elasticity,  moving  through  a  greater  space  than  the  centre  of 
the  wing.  By  fixing  the  wing  to  the  head  of  the  piston  all 


AEKONAUTICS.  245 

gearing  apparatus  is  avoided,  and  the  number  of  joints  and 
working  points  reduced — a  matter  of  no  small  importance 
when  it  is  desirable  to  conserve  the  motor  power  and  keep 
down  the  weight. 

How  to  apply  Artificial  Wings  to  the  Air. — Borelli, 
Durckheim,  Marey,  and  all  the  writers  with  whom  I  am 
acquainted,  assert  that  the  wing  should  be  made  to  vibrate 
vertically.  I  believe  that  if  the  wing  be  in  one  piece  it 
should  be  made  to  vibrate  obliquely  and  more,  or  less  horizon- 
tally. If,  however,  the  wing  be  made  to  vibrate  vertically, 
it  is  necessary  to  supply  it  with  a  ball-and-socket  joint,  and 
with  springs  at  its  root  (m  n  of  fig.  125,  p.  241),  to  enable  it 
to  leap  forward  in  a  curve  when  it  descends,  and  in  another 
and  opposite  curve  when  it  ascends  (vide  a,  c,e,  g,i  of  fig.  81, 
p.  157).  This  arrangement  practically  converts  the  vertical 
vibration  into  an  oblique  one.  If  this  plan  be  not  adopted, 
the  wing  is  apt  to  foul  at  its  tip.  In  applying  the  wing  to 
the  air  it  ought  to  have  a  figure-of-8  movement  communicated 
to  it  either  directly  or  indirectly.  It  is  a  peculiarity  of  the 
artificial  wing  properly  constructed  (as  it  is  of  the  natural 
wing),  tJiat  it  twists  and  untwists  and  makes  figure-of-S  curves 
during  its  action  (see  a  b,  cd  of  fig.  122,  p.  239),  this  enabling 
it  to  seize  and  let  go  the  air  with  wonderful  rapidity,  and 
in  such  a  manner  as  to  avoid  dead  points.  If  the  wing  be 
in  several  pieces,  it  may  be  made  to  vibrate  more  vertically 
than  a  wing  in  one  piece,  from  the  fact  that  the  outer  half 
of  the  pinion  moves  forwards  and  backwards  when  the  wing 
ascends  and  descends  so  as  alternately  to  become  a  short  and 
a  long  lever ;  this  arrangement  permitting  the  wing  to  avoid 
the  resistance  experienced  from  the  air  during  the  up  stroke, 
while  it  vigorously  seizes  the  air  during  the  down  stroke. 

If  the  body  of  a  flying  animal  be  in  a  horizontal  position, 
a  wing  attached  to  it  in  such  a  manner  that  its  under  surface 
shall  look  forwards,  and  make  an  upward  angle  of  45°  with 
the  horizon  is  in  a  position  to  be  applied  either  vertically 
(figs.  82  and  83,  p.  158),  or  horizontally  (figs.  67,  68,  69,  and 
70,  p.  141).  Such,  moreover,  is  the  conformation  of  the 
shoulder-joint  in  insects,  bats,  and  birds,  that  the  wing  can 
be  applied  vertically,  horizontally,  or  at  any  degree  of  obliquity 


246  AERONAUTICS. 

without  inconvenience.1  It  is  in  this  way  that  an  insect 
which  may  begin  its  flight  by  causing  its  wings  to  make 
figure-of-8  horizontal  loops  (fig.  71,  p.  144),  may  gradu- 
ally change  the  direction  of  the  loops,  and  make  them  more 
and  more  oblique  until  they  are  nearly  vertical  (fig.  73,  p. 
144).  In  the  beginning  of  such  flight  the  insect  is  screwed 
nearly  vertically  upwards;  in  the  middle  of  it,  it  is  screwed 
upwards  and  forwards:  whereas,  towards  the  end  of  it,  the 
insect  advances  in  a  ^caved  line  almost  horizontally  (see 
tf,r',s',t'  of  fig.  72,  p.  144).  The  muscles  of  .the  wing  are 
so  arranged  that  they  can  propel  it  in  a  horizontal,  vertical, 
or  oblique  direction.  It  is  a  matter  of  the  utmost  importance 
that  the  direction  of  the  stroke  and  the  nature  of  the  angles 
made  by  the  surface  of  the  wing  during  its  vibration  with 
the  horizon  be  distinctly  understood ;  as  it  is  on  these  that 
all  flying  creatures  depend  when  they  seek  to  elude  the  up- 
ward resistance  of  the  air,  and  secure  a  maximum  of  elevating 
and  propelling  power  with  a  minimum  of  slip. 

As  to  the  nature  of  the  Forces  required  for  propelling  Arti- 
ficial Wings. — Borelli,  Durckheim,  and  Marey  affirm  that  it 
suffices  if  the  wing  merely  elevates  and  depresses  itself  by 
a  rhythmical  movement  in  a  perpendicular  direction ;  while 
Chabrier  is  of  opinion  that  a  movement  of  depression  only  is 
required.  All  those  observers  agree  in  believing  that  the 
details  of  flight  are  due  to  the  reaction  of  the  air  on  the  sur- 
face of  the  wing.  Eepeated  experiment  has,  however,  con- 
vinced me  that  the  artificial  wing  must  be  thoroughly  under 
control,  both  during  the  down  and  up  strokes — the  details  of 
flight  being  in  a  great  measure  due  to  the  movements  com- 
municated to  the  wing  by  an  intelligent  agent.  In  order 
to  reproduce  flight  by  the  aid  of  artificial  wings,  I  find  it 
necessary  to  employ  a  power  which  varies  in  intensity  at 
every  stage  of  the  down  and  up  strokes.  The  power  which 

1  The  human  wrist  is  so  formed  that  if  a  wing  be  held  in  the  hand  at  an 
upward  angle  of  45°,  the  hand  can  apply  it  to  the  air  in  a  vertical  or  horizontal 
direction  without  difficulty.  This  arises  from  the  power  which  the  hand  has 
of  moving  in  an  upward  and  downward  direction,  and  from  side  to  side  with 
equal  facility.  The  hand  can  also  rotate  on  its  long  axis,  so  that  it  virtually 
represents  all  the  movements  of  the  wing  at  its  root. 


AERONAUTICS.  247 

suits  best  is  one  which  is  made  to  act  very  suddenly  and 
forcibly  at  the  beginning  of  the  down  stroke,  and  which  gradu- 
ally abates  in  intensity  until  the  end  of  the  down  stroke,  where 
it  ceases  to  act  in  a  downward  direction.  The  power  is  then 
made  to  act  in  an  upward  direction,  and  gradually  to  decrease 
until  the  end  of  the  up  stroke.  The  force  is  thus  applied 
more  or  less  continuously ;  its  energy  being  increased  and 
diminished  according  to  the  position  of  the  wing,  and  the 
amount  of  resistance  which  it  experiences  from  the  air.  The 
flexible  and  elastic  nature  of  the  wave  wing,  assisted  by 
certain  springs  to  be  presently  explained,  insure  a  continuous 
vibration  where  neither  halts  nor  dead  points  are  observ- 
able. I  obtain  the  varying  power  required  by  a  direct  piston 
action,  and  by  working  the  steam  expansively.  The  power 
employed  is  materially  assisted,  particularly  during  the  up 
stroke,  by  the  reaction  of  the  air  and  the  elastic  struc- 
tures about  to  be  described.  An  artificial  wing,  propelled 
and  regulated  by  the  forces  recommended,  is  in  some 
respects  as  completely  under  control  as  the  wing  of  the 
insect,  bat,  or  bird. 

Necessity  for  supplying  tJie  Root  of  Artificial  Wings  with 
Elastic  Structures  in  imitation  of  tJie  Muscles  and  Elastic  Liga- 
ments of  Flying  Animals. — Borelli,  Durckheim,  and  Marey, 
who  advocate  the  perpendicular  vibration  of  the  wing,  make 
no  allowance,  so  far  as  I  am  aware,  for  the  wing  leaping 
forward  in  curves  during  tJie  down  and  up  strokes.  As  a  con- 
sequence, the  wing  is  jointed  in  their  models  to  the  frame 
by  a  simple  joint  which  moves  only  in  one  direction,  viz., 
from  above  downwards,  and  vice  versa.  Observation  and 
experiment  have  fully  satisfied  me  that  an  artificial  wing, 
to  be  effective  as  an  elevator  and  propeller,  ought  to  be 
able  to  move  not  only  in  an  upward  and  downward  direc- 
tion, but  also  in  a  forward,  backward,  and  oblique  direction ; 
nay,  more,  that  it  should  be  free  to  rotate  along  its  anterior 
margin  in  the  direction  of  its  length ;  in  fact,  that  its  move- 
ments should  be  universal.  Thus  it  should  be  able  to  rise  or 
fall,  to  advance  or  retire,  to  move  at  any  degree  of  obliquity, 
and  to  rotate  along  its  anterior  margin.  To  secure  the 
several  movements  referred  to  I  furnish  the  root  of  the  wing 


248  AERONAUTICS. 

with  a  ball-and-socket  joint,  i.e.,  a  universal  joint  (see  x  of 
fig.  122,  p.  239).  To  regulate  the  several  movements  when 
the  wing  is  vibrating,  and  to  confer  on  the  wing  the  various 
inclined  surfaces  requisite  for  flight,- as  well  as  to  delegate 
as  little  as  possible  to  the  air,  I  employ  a  cross  system  of 
elastic  bands.  These  bands  vary  in  length,  strength,  and 
direction,  and  are  attached  to  the  anterior  margin  of  the  wing 
(near  its  root),  and  to  the  cylinder  (or  a  rod  extending 
from  the  cylinder)  of  the  model  (vide  m,n  of  fig.  122,  p. 
239).  The  principal  bands  are  four  in  number — a  superior, 
inferior,  anterior,  and  posterior.  The  superior  band  (m) 
extends  between  the  upper  part  of  the  cylinder  of  the 
model,  and  the  upper  surface  of  the  anterior  margin  of  the 
wing ;  the  inferior  band  (ri)  extending  between  the  under  part 
of  the  cylinder  or  the  boiler  and  the  inferior  surface  of  the 
anterior  margin  of  the  pinion.  The  anterior  and  posterior 
bands  are  attached  to  the  anterior  and  posterior  portions  of 
the  wing  and  to  rods  extending  from  the  centre  of  the 
anterior  and  posterior  portions  of  the  cylinder.  Oblique 
bands  are  added,  and  these  are  so  arranged  that  they  give  to 
the  wing  during  its  descent  and  ascent  the  precise  angles 
made  by  the  wing  with  the  horizon  in  natural  flight.  The 
superior  bands  are  stronger  than  the  inferior  ones,  and  are 
put  upon  the  stretch  during  the  down  stroke.  Thus  they 
help  the  wing  over  the  dead  point  at  the  end  of  the  down 
stroke,  and  assist,  in  conjunction  with  the  reaction  obtained 
from  the  air,  in  elevating  it.  The  posterior  bands  are 
stronger  than  the  anterior  ones  to  restrain  within  certain 
limits  the  great  tendency  which  the  wing  has  to  leap  forward 
in  curves  towards  the  end  of  the  down  and  up  strokes.  The 
oblique  bands,  aided  by  the  air,  give  the  necessary  degree  of 
rotation  to  the  wing  in  the  direction  of  its  length.  This 
effect  can,  however,  also  be  produced  independently  by  the 
four  principal  bands.  From  what  has  been  stated  it  will  be 
evident  that  the  elastic  bands  exercise  a  restraining  influence, 
and  that'  they  act  in  unison  with  the  driving  power  and  with 
the  reaction  supplied  by  the  air.  They  powerfully  contribute 
to  the  continuous  vibration  of  the  wing,  the  vibration  being 
peculiar  in  this  that  it  varies  in  rapidity  at  every  stage  of  the 


AERONAUTICS.  249 

down  and  up  strokes.  I  derive  the  motor  power,  as  has  been 
stated,  from  a  direct  piston  action,  the  piston  being  urged  either 
by  steam  worked  expansively  or  by  the  hand,  if  it  is  merely  a 
question  of  illustration.  In  the  hand  models  the  "  muscular 
sense  "  at  once  informs  the  operator  as  to  what  is  being  done. 
Thus  if  one  of  the  wave  wings  supplied  with  a  ball-and-socket 
joint,  and  a  cross  system  of  elastic  bands  as  explained,  has  a 
sudden  vertical  impulse  communicated  to  it  at  the  beginning  of 
the  down  stroke,  the  wing  darts  downwards  and  forwards  in 
a  curve  (vide  a  c,  of  fig.  81,  p.  157),  and  in  doing  so  it  elevates 
and  carries  the  piston  and  cylinder  forwards.  The  force 
employed  in  depressing  the  wing  is  partly  expended  in 
stretching  the  superior  elastic  band,  the  wing  being  slowed 
towards  the  end  of  the  down  stroke.  The  instant  the  depress- 
ing force  ceases  to  act,  the  superior  elastic  band  contracts  and 
the  air  reacts ;  the  two  together,  coupled  with  the  tendency 
which  the  model  has  to  fall  downwards  and  forwards  during 
the  up  stroke,  elevating  the  wing.  The  wing  when  it  ascends 
describes  an  upward  and  forward  curve  as  shown  at  ce  of 
fig.  81,  p.  157.  The  ascent  of  the  wing  stretches  the  inferior 
elastic  band  in  the  same  way  that  the  descent  of  the  wing 
stretched  the  superior  band.  The  superior  and  inferior 
elastic  bands  antagonize  each  other  and  reciprocate  with 
vivacity.  While  those  changes  are  occurring  the  wing  is 
twisting  and  untwisting  in  the  direction  of  its  length  and 
developing  figure-of-8  curves  along  its  margins  (p.  239,  fig. 
122,ab,cd),  and  throughout  its  substance  similar  to  what 
are  observed  under  like  circumstances  in  the  natural  wing 
(vide  fig.  86,  p.  161 ;  fig.  103,  p.  186).  The  angles,  moreover, 
made  by  the  under  surface  of  the  wing  with  the  horizon 
during  the  down  and  up  strokes  are  continually  varying — the 
wing  all  the  while  acting  as  a  kite,  which  flies  steadily 
upwards  and  forwards  (fig.  88,  p.  166).  As  the  elastic 
bands,  as  has  been  partly  explained,  are  antagonistic  in  their 
action,  the  wing  is  constantly  oscillating  in  some  direction; 
there  being  no  dead  point  either  at  the  end  of  the  down  or 
up  strokes.  As  a  consequence,  the  curves  made  by  the  wing 
during  the  down  and  up  strokes  respectively,  run  into  each 
other  to  form  a  continuous  waved  track,  as  represented  at  fig. 
12 


250 


AERONAUTICS. 


81,  p.  157,  and  fig.  88,  p.  166.  A  continuous  movement 
begets  a  continuous  buoyancy ;  and  it  is  quite  remarkable  to 
what  an  extent,  wings  constructed  and  applied  to  the  air 
on  the  principles  explained,  elevate  and  propel — how  little 
power  is  required,  and  how  little  of  that  power  is  wasted  in 
slip. 

If  the  piston,  which  in  the  experiment  described  has  been 
working  Vertically,  be  made  to  work  horizontally,  a  series  of 
essentially  similar  results  are  obtained.  When  the  piston' 
is  worked  horizontally,  the  anterior  and  posterior  elastic 
bands  require  to  be  of  nearly  the  same  strength,  whereas 
the  inferior  elastic  baud  requires  to  be  much  stronger 
than  the  superior  one,  to  counteract  the  very  decided  ten- 
dency the  wing  has  to  fly  upwards.  The  power  also  requires 


d  cl 


FIG.  127. 


FIG.  127. — Path  described  by  artificial  wave  wing  from  right  to  left,  x,  yf, 
Horizon,  m,  n,  o,  Wave  track  traversed  by  wing  from  right  to  left,  p, 
Angle  made  by  the  wing  with  the  horizon  at  beginning  of  stroke,  q,  Ditto, 
made  at  middle  of  stroke,  b,  Ditto,  towards  end  of  stroke.  c,  Wing  in 
the  act  of  reversing  ;  at  this  stage  the  wing  makes  an  angle  of  90"  with  the 
horizon,  and  its  speed  is  less  than  at  any  other  part  of  its  course,  d,  Wing 
reversed,  and  in  the  act  of  darting  up  to  u,  to  begin  the  stroke  from  left  to 
right  (vide  u  of  fig.  128).—  Original. 

FIG.  128.— Path  described  by  artificial  wave  wing  from  left  to  right,  x,  of, 
Hori/on.  u,  v,  w,  Wave,  track  traversed  by  wing  from  left  to  right.  t, 
Angle  made  by  the  wing  with  horizon  at  beginning  of  stroke,  y,  Ditto, 
at  middle  of  stroke.  2,  Ditto,  towards  end  of  stroke,  r,  Wing  in  the  act 
of  reversing  ;  at  this  stage  the  wing  makes  an  angle  of  90°  with  the  horizon, 
and  its  speed  is  less  that  at  any  other  part  of  its  course,  s,  Wing  reversed, 
and  in  the  act  of  darting  up  to  in,  to  begin  the  stroke  from  right  to  left  ^rulc 
m  of  fig.  127). — Original. 

to  be  somewhat  differently  applied.  Thus  the  wing  must 
have  a  violent  impulse  communicated  to  it  when  it  begins  the 
stroke  from  right  to  left,  and  also  when  it  begins  -the  stroke 
from  left  to  right  (the  heavy  parts  of  the  spiral  line  repre- 
sented at  fig.  71,  p.  144,  indicate  the  points  where  the  impulse 
is  communicated).  The  wing  is  then  left  to  itself,  the  elastic 
bands  and  the  reaction  of  the  air  doing  the  remainder  of  the 
work.  When  the  wing  is  forced  by  the  piston  from  right  to 


AERONAUTICS.  251 

left,  it  darts  forward  in  double  curve,  as  shown  at  fig.  127; 
the  various  inclined  surfaces  made  by  the  wing  with  the 
horizon  changing  at  every  stage  of  the  stroke. 

At  the  beginning  of  the  stroke  from  right  to  left,  the  angle 
made  by  the  under  surface  of  the  wing  with  the  horizon  (xx) 
is  something  like  45°  (p),  whereas  at  the  middle  of  the  stroke  it 
is  reduced  to  20°  or  25°  (q).  At  the  end  of  the  stroke  the  angle 
gradually  increases  to  45°  (£>),  then  to  90°  (c),  after  which  the 
wing  suddenly  turns  a  somersault  (d),  and  reverses  precisely  as 
the  natural  wing  does  at  e,f,  g  of  figs.  67  and  69,  p.  141.  The 
artificial  wing  reverses  with  amazing  facility,  and  in  the  most 
natural  manner  possible.  The  angles  made  by  its  under 
surface  with  the  horizon  depend  chiefly  upon  the  speed  with 
which  the  wing  is  urged  at  different  stages  of  the  stroke ;  the 
angle  always  decreasing  as  the  speed  increases,  and  vice  versa. 
As  a  consequence,  the  angle  is  greatest  when  the  speed  is  least. 

When  the  wing  reaches  the  point  b  its  speed  is  much  less 
than  it  was  at  q.  The  wing  is,  in  fact,  preparing  to  reverse. 
At  c  the  wing  is  in  the  act  of  reversing  (compare  c  of  figs.  84 
and  85,  p.  160),  and,  as  a  consequence,  its  speed  is  at  a 
minimum,  and  the  angle  which  it  makes  with  the  horizon  at 
a  maximum.  At  d  the  wing  is  reversed,  its  speed  being 
increased,  and  the  angle  which  it  makes  with  the  horizon 
diminished.  Between  the  letters  d  and  u  the  wing  darts 
suddenly  up  like  a  kite,  and  at  u  it  is  in  a  position  to  com- 
mence the  stroke  from  left  to  right,  as  indicated  at  u  of  fig. 
128,  p.  250.  The  course  described  and  the  angles  made  by 
the  wing  with  the  horizon  during  the  stroke  from  left  to 
right  are  represented  at  fig.  128  (compare  with  figs.  68  ami 
70,  p.  141).  The  stroke  from  left  to  right  is  in  every  respect 
the  converse  of  the  stroke  from  right  to  left,  so  that  a  separate 
description  is  unnecessary. 

The  Artificial  Wave  Wing  can  be  driven  at  any  speed- 
it  can  make  its  own  currents,  or  utilize  existing  ones. — The 
remarkable  feature  in  the  artificial  wave  wing  is  its  adapta- 
bility. It  can  be  driven  slowly,  or  with  astonishing  rapidity. 
It  lias  no  dead  points.  It  reverses  instantly,  and  in  such  n 
manner  as  to  dissipate  neither  time  nor  power.  It  alternately 
*  seizes  and  evades  the  air  so  as  to  extract  the  maximum 


253  AERONAUTICS. 

of  support  with  the  minimum  of  slip,  and  the  minimum 
of  force.  It  supplies  j,  degree  of  buoying  and  propelling 
power  which  is  truly  remarkable.  Its  buoying  area  is 
nearly  equal  to  half  a  circle.  It  can  act  upon  still  air, 
and  it  can  create  and  utilize  its  own  currents.  I  proved  this 
in  the  following  manner.  I  caused  the  wing  to  make  a 
horizontal  sweep  from  right  to  left  over  a  candle ;  the  wing 
rose  steadily  as  a  kite  would,  and  after  a  brief  interval,  the 
flame  of  the  candle  was  persistently  blown  from  right  to  left. 
I  then  waited  until  the  flame  of  the  candle  assumed  its 
normal  perpendicular  position,  after  which  I  caused  the  wing 
to  make  another  and  opposite  sweep  from  left  to  right.  The 
wing  again  rose  kite  fashion,  and  the  flame  was  a  second  time 
affected,  being  blown  in  this  case  from  left  to  right.  I  now 
caused  the  wing  to  vibrate  steadily  and  rapidly  above  the 
candle,  with  this  curious  result,  that  the  flame  did  not  incline 
alternately  from  right  to  left  and  from  left  to  right.  On  the 
contrary,  it  was  blown  steadily  away  from  me,  i.e.  in  the 
direction  of  the  tip  of  the  wing,  thus  showing  that  the  arti- 
ficial currents  made  by  the  wing,  met  and  neutralized  each 
other  always  at  mid  stroke.  I  also  found  that  under  these 
circumstances  the  buoying  power  of  the  wing  was  remarkably 
increased. 

Compound  rotation  of  the  Artificial  Wave  Wing :  the  different 
1  arts  of  the  Wing  travel  at  different  speeds. — The  artificial 
wave  wing,  like  the  natural  wing,  revolves  upon  two  centres 
(ab,  cd  of  fig.  80,  p.  149;  fig.  83,  p.  158,  and  fig.  122, 
p.  239),  and  owes  much  of  its  elevating  and  propelling, 
seizing,  and  disentangling  power  to  its  different  portions 
travelling  at  different  rates  of  speed  (see  fig.  56,  p.  120),  and 
to  its  storing  up  and  giving  off  energy  as  it  hastens  to  and 
fro.  Thus  the  tip  of  the  wing  moves  through  a  very  much 
greater  space  in  a  given  time  than  the  root,  and  so  also  of  the 
posterior  margin  as  compared  with  the  anterior.  This  is 
readily  understood  by  bearing  in  mind  that  the  root  of  the 
wing  forms  the  centre  or  axis  of  rotation  for  the  tip,  while 
the  anterior  margin  is  the  centre  or  axis  of  rotation  for  the 
posterior  margin.  The  momentum,  moreover,  acquired  by 
the  wing  /luring  the  stroke  from  right  to  left  is  expended  Of 


AERONAUTICS. 


253 


reversing  tlie  wing,  and  in  preparing  it  for  the  stroke  from 
left  to  right,  and  vice  versa  ;  a  continuous  to-and-fro  move- 
ment devoid  of  dead  points  being  thus  established.  If  the 
artificial  wave  wing  be  taken  in  the  hand  and  suddenly  de- 
"  pressed  in  a  more  or  less  vertical  direction,  it  immediately 
springs  up  again,  and  carries  the  hand  with  it.  It,  in  fact, 
describes  a  curve  whose  convexity  is  directed  downwards,  and 
in  doing  so,  carries  the  hand  upwards  and  forwards.  If  a 
second  down  stroke  be  added,  a  second  curve  is  formed  ;  the 
curves  running  into  each  other,  and  producing  a  progressive 
waved  track  similar  to  what  is  represen  ted  at  a,  c,  e,  g,  i,  of 
fig.  81,  p.  157.  This  result  is  favoured  if  the  operator  runs 
forward  so  as  not  to  impede  or  limit  the  action  of  the  wing. 

How  tJie  Wave  Wing  creates  currents,  and  rises  u\wn,  them, 
and  how  the  Air  assists  in  elevating  the  Wing. — In  order  to 
ascertain  in  what  way  the  air  contributes  to  the  elevation 
of  the  wing,  I  made  a  series  of  experiments  with  natural 


FIG.  129. 


j'.nd  artificial  wings.  These  experiments  led  me  to  conclude 
that  when  the  wing  descends,  as  in  the  bat  and  bml.  it 
compresses  and  pushes  before  it,  in  a  downward  and  forward 


254  AERONAUTICS. 

direction,  a  column  of  air  represented  by  a,  b,  c  of  fig.  129,  p. 
25  3.1  The  air  rushes  in  from  all  sides  to  replace  the  dis- 
placed air,  as  shown  at  d,e,f,g,h,i,  and  so  produces  a  circle 
of  motion  indicated  by  the  dotted  line  s,  t,  v,  w.  The  wing 
rises  upon  the  outside  of  the  circle  referred  to,  as  more  par- 
ticularly seen  at  d,  e,  v,  w.  The  arrows,  it  will  be  observed, 
are  all  pointing  upwards,  and  as  these  arrows  indicate  the 
direction  of  the  reflex  or  back  current,  it  is  not  difficult 
to  comprehend  how  the  air  comes  indirectly  to  assist  in 
elevating  the  wing.  A  similar  current  is  produced  to  the 
right  of  the  figure,  as  indicated  by  I,  m,  o,  p,  q,  r,  but  seeing 
the  wing  is  always  advancing,  this  need  not  be  taken  into 
account. 

If  fig.  129  be  made  to  assume  a  horizontal  position,  in- 
stead of  the  oblique  position  which  it  at  present  occupies, 
the  manner  in  which  an  artificial  current  is  produced  by 
one  sweep  of  the  wing  from  right  to  left,  and  utilized  by  it 
in  a  subsequent  sweep  from  left  to  right,  will  be  readily 
understood.  The  artificial  wave  wing  makes  a  horizontal 
sweep  from  right  to  left,  i.e.  it  passes  from  the  point  a  to  the 
point  c  of  fig.  129.  During  its  passage  it  has  displaced  a 
column  of  air.  To  fill  the  void  so  created,  the  air  rushes  in 
from  all  sides,  viz.  from  d,e,f,ff,h,i;  l,m,o,p,q,r.  The 
currents  marked  g,  h,  i  ;  p,  q,  r,  represent  the  reflex  or  arti- 
ficial currents.  These  are  the  currents  which,  after  a  brief 
interval,  force  the  flame  of  the  candle  from  right  to  left.  It 
is  those  same  currents  which  the  wing  encounters,  and  which 
contribute  so  powerfully  to  its  elevation,  when  it  sweeps  from 
left  to  right.  The  wing,  when  it  rushes  from  left  to  right, 
produces  a  new  series  of  artificial  currents,  which  are  equally 
powerful  in  elevating  the  wing  when  it  passes  a  second  time 
from  right  to  left,  and  thus  the  process  of  making  and 
utilizing  currents  goes  on  so  long  as  the  wing  is  made  to 
oscillate.  In  waving  the  artificial  wing  to  and  fro,  I  found 

1  The  artificial  currents  produced  by  the  wing  during  its  descent  may  he 
readily  seen  by  partially  filling  a  chamber  with  steam,  smoke,  or  some  impal- 
pable white  powder,  and  causing  the  Aving  to  descend  in  its  midst.  By  a 
little  practice,  the  eye  will  not  fail  to  detect  the  currents  represented  at 
d,  e,  f,  (J,  h,  i,  I,  m,  o,  p,  g,  r  of  fig.  129,  p.  253. 


AERONAUTICS.  255 

the  best  results  were  obtained  when  the  range  of  the  wing 
and  the  speed  with  which  it  was  urged  were  so  regulated  as 
to  produce  a  perfect  reciprocation.  Thus,  if  the  range  of  the 
wing  be  great,  the  speed  should  also  be  high,  otherwise  the 
air  set  in  motion  by  the  right  stroke  will  not  be  utilized  by 
the  left  stroke,  and  vice  versd.  If,  on  the  other  hand,  the 
range  of  the  wing  be  small,  the  speed  should  also  be  low,  as 
the  short  stroke  will  enable  the  wing  to  reciprocate  as  per- 
fectly as  when  the  stroke  is  longer  and  the  speed  quicker. 
When  the  speed  attained  is  high,  the  angles  made  by  the 
under  surface  of  the  wing  with  the  horizon  are  diminished ; 
when  it  is  low,  the  angles  are  increased.  From  these  re- 
marks it  will  be  evident  that  the  artificial  wave  wing  reci- 
procates in  the  same  way  that  the  natural  wing  reciprocates ; 
the  reciprocation  being  most  perfect  when  the  wing  is 
vibrating  in  a  given  spot,  and  least  perfect  when  it  is  travel- 
ling at  a  high  horizontal  speed. 

The  Artificial  Wing  propelled  at  various  degrees  of  speed 
during  the  Dawn  and  Up  Strokes. — The  tendency  which  the 
artificial  wave  wing  has  to  rise  again  when  suddenly  and 
vigorously  depressed,  explains  why  the  elevator  muscles  of 
the  wing  should  be  so  small  when  compared  with  the  depressor 
muscles — the  latter  being  something  like  seven  times  larger 
than  the  former.  That  the  contraction  of  the  elevator 
muscles  is  necessary  to  the  elevation  of  the  wing,  is  abun- 
dantly proved  by  their  presence,  and  that  there  should  be  so 
great  a  difference  between  the  volume  of  the  elevator  and 
depressor  muscles  is  not  to  be  wondered  at,  when  we  remem- 
ber that  the  whole  weight  of  the  body  is  to  be  elevated  by 
the  rapid  descent  of  the  wings — the  descent  of  the  wing 
being  entirely  due  to  the  vigorous  contraction  of  the  powerful 
pectoral  muscles.  If,  however,  the  wing  was  elevated  with 
as  great  a  force  as  it  was  depressed,  no  advantage  would  be 
gained,  as  the  wing,  during  its  ascent  (it  acts  against 
gravity)  would  experience  a  much  greater  resistance  from 
the  air  than  it  did  during  its  descent.  The  wing  is  con- 
sequently elevated  more  slowly  than  it  is  depressed ;  the 
elevator  muscles  exercising  a  controlling  and  restraining 
influence.  By  slowing  the  wing  during  the  up  stroke, 


256  AERONAUTICS. 

the  air  has  an  opportunity  of  reacting  on  its  under  sur- 
face. 

The  Artificial  Wave  Wing  as  a  Propeller. — The  wave 
wing  makes  an  admirable  propeller  if  its  tip  be  directed 
vertically  downwards,  and  the  wing  lashed  from  side  to  side 
with  a  sculling  figure-of-8  motion,  similar  to  that  executed  by 
the  tail  of  the  fish.  Three  wave  wings  may  be  made  to  act 
in  concert,  and  with  a  very  good  result ;  two  of  them  being 
made  to  vibrate  figure-of-8  fashion  in  a  more  or  less  horizontal 
direction  with  a  view  to  elevating ;  the  third  being  turned  in 
a  downward  direction,  and  made  to  act  vertically  for  the 
purpose  of  propelling. 


FIG.  130.-- Aerial  wave  screw,  whose  blades  are  slightly  twisted  (ab,cd; 
ef,gh),  so  that  those  portions  nearest  the  root  (rf/i)  make  a  greater  angle 
with  the  horizon  than  those  parts  nearer  the  tip  (bf).  The  angle  is  thus 
adjusted  to  the  speed  attained  by  the  different  portions  of  the  screw.  The 
angle  admits  of  further  adjustment  by  means  of  the  steel  springs  z,  s, 
these  exercising  a  -estraining,  and  to  a  certain  extent  a  regulating,  influ- 
ence which  effectually  prerents  shock. 

It  will  be  atonce  perceived  from  this  figure  that  the  portions  of  the  screw 
marked  m  and  n  travel  at  a  much  lower  speed  than  those  portions  marked 
o  and  p,  and  these  again  more  slowly  than  those  marked  q  and  r  (compare 
with  tig.  56,  p.  120).  As,  however,  the  angle  which  a  wing  or  a  portion  of 
a  wing,  as  1  have  pointed  out,  varies  to  accommodate  itself  to  the  speed 
attained  by  the  wing,  or  a  portion  thereof,  it  follows,  that  to  make  the  wave 
screw  mechanically  perfect,  the  angles  made  by  its  several  portions  must 
be  accurately  adapted  to  the  travel  of  its  several  parts  as  indicated  above. 

x,  Vertical  tube  for  receiving  driving  shaft,  v,  ^v,  Sockets  in  which  the 
roots  of  the  blades  of  the  screw  rotate,  the  degree  of  rotation  being  limited 
by  the  steel  springs  z,  s.  a  b,  ef,  Taptring  elastic  reeds  forming  anterior  or 
thick  margins  of  blades  of  screw,  d  c,  hg,  Posterior  or  thin  elastic  margins 
of  blades  of  screw,  m  n,  op,qr,  Radii  formed  by  the  different  portions  of 
the  blades  of  the  screw  when  in  operation.  The  arrows  indicate  the  direc- 
tion of  travel.— Original. 

A  New  Form  of  Aerial  Screw. — If  two  of  the  wave  wings 
represented  at  fig.  122,  p.  239,  be  placed  end  to  end,  and 
united  to  a  vertical  portion  of  tube  to  form  a  two-bladed 
screw,  similar  to  that  employed  in  navigation,  a  most  powerful 
elastic  aerial  screw  is  at  once  produced,  as  seen  at  fig.  130. 


AERONAUTICS.  257 

This  screw,  which  for  the  sake  of  uniformity  I  denominate 
the  aerial  wave  screw,  possesses  advantages  for  aerial  pur- 
poses to  which  no  form  of  rigid  screw  yet  devised  can  lay 
claim.  The  way  in  which  it  clings  to  the  air  during  its 
revolution,  and  the  degree  of  buoying  power  it  possesses,  are 
quite  astonishing.  It  is  a  self-adjusting,  self-regulating  screw, 
and  as  its  component  parts  are  flexible  and  elastic,  it  accom- 
modates itself  to  the  speed  at  which  it  is  driven,  and  gives 
a  uniform  buoyancy.  The  slip,  I  may  add,  is  nominal  in 
amount.  This  screw  is  exceedingly  light,  and  owes  its  efficacy 
to  its  shape  and  the  graduated  nature  of  its  blades;  the 
anterior  margin  of  each  blade  being  comparatively  rigid, 
the  posterior  margin  being  comparatively  flexible  and 
more  or  less  elastic.  The  blades  are  kites  in  the  same 
sense  that  natural  wings  are  kites.  They  are  flown  as  such 
when  the  screw  revolves.  I  find  that  the  aerial  wave  screw 
flies  best  and  elevates  most  when  its  blades  are  inclined  at  a 
certain  upward  angle  as  indicated  in  the  figure  (130).  The 
aerial  wave  screw  may  have  the  number  of  its  blades  in- 
creased by  placing  the  one  above  the  other ;  and  two  or  more 
screws  may  be  combined  and  made  to  revolve  in  opposite 
directions  so  as  to  make  them  reciprocate;  the  one  screw  pro- 
ducing the  current  on  which  the  other  rises,  as  happens  in 
natural  wings. 

The  Aerial  Wave  Screw  operates  also  upon  Water. — The 
form  of  screw  just  described  is  adapted  in  a  marked  manner 
for  water,  if  the  blades  be  reduced  in  size  and  composed  of 
some  elastic  substance,  which  will  resist  the  action  of  fluids, 
as  gutta-percha,  carefully  tempered  finely  graduated  steel  plates, 
etc.  It  bears  the  same  relation  to,  and  produces  the  same 
results  upon,  water,  as  the  tail  and  fin  of  the  fish.  It  throws 
its  blades  during  its  action  into  double  figure-of-8  curves, 
similar  in  all  respects  to  those  produced  on  the  anterior  and 
posterior  margins  of  the  natural  and  artificial  flying  wing.  As 
the  speed  attained  by  the  several  portions  of  each  blade  varies, 
so  the  angle  at  which' each  part  of  the  blade  strikes  varies; 
the  angles  being  always  greatest  towards  the  root  of  the  blade 
and  least  towards  the  tip.  The  angles  made  by  the  different 
portions  of  the  blades  are  diminished  in  proportion  as  the 


258  AERONAUTICS. 

speed,  with  which  the  screw  is  driven,  is  increased.  The 
screw  in  this  manner  is  self-adjusting,  and  extracts  a  large 
percentage  of  propelling  power,  with  very  little  force  and 
surprisingly  little  slip. 

A  similar  result  is  obtained  if  two  finely  graduated  angular- 
shaped  gutta-percha  or  steel  plates  be  placed  end  to  end  and 
applied  to  the  water  (vertically  or  horizontally  matters  little), 
with  a  slight  sculling  figure-of-8  motion,  analogous  to  that 
performed  by  the  tail  of  the  fish,  porpoise,  or  whale.  If  the 
thick  margin  of  the  plates  be  directed  forwards,  and  the 
thin  ones  backward,0,,  an  unusually  effective  propeller  is  pro- 
duced. This  form  of  propeller  is  likewise  very  effective  in  air. 


CONCLUDING   EEMAEKS. 

FROM  the  researches  and  experiments  detailed  in  the  pre- 
sent volume,  it  will  be  evident  that  a  remarkable  analogy 
exists  between  walking,  swimming,  and  flying.  It  will 
further  appear  that  the  movements  of  the  tail  of  the  fish,  and 
of  the  wing  of  the  insect,  bat,  and  bird  can  be  readily  imi- 
tated and  reproduced.  These  facts  ought  to  inspire  the 
pioneer  in  aerial  navigation  with  confidence.  The  land  and 
water  have  already  been  successfully  subjugated.  The  realms 
of  the  air  alone  are  unvanquished.  These,  however,  are  so 
vast  and  so  important  as  a  highway  for  the  nations,  that 
science  and  civilisation  equally  demand  their  occupation. 
The  history  of  artificial  progression  indorses  the  belief  that 
the  fields  etherean  will  one  day  be  traversed  by  a  machine 
designed  by  human  ingenuity,  and  constructed  by  human 
skill.  In  order  to  construct  a  successful  flying  machine,  it  is 
not  necessary  to  reproduce  the  filmy  wing  of  the  insect,  the 
silken  pinion  of  the  bat,  or  the  complicated  and  highly  differ- 
entiated wing  of  the  bird,  where  every  feather  may  be  said 


AERONAUTICS.  259 

to  have  a  peculiar  function  assigned  to  it ;  neither  is  it  neces- 
sary to  reproduce  the  intricacy  of  that  machinery  by  which 
the  pinion  in  the  bat,  insect,  and  bird  is  moved  :  all  that  is 
required  is  to  distinguish  the  properties,  form,  extent,  and 
manner  of  application  of  the  several  flying  surfaces,  a  task 
attempted,  however  imperfectly  executed,  in  the  foregoing 
pages.     When  Vivian   and  Trevithick  devised  the   locomo- 
tive,  and    Symington   and    Bell   the   steamboat,   they   did 
not  seek  to  reproduce  a  quadruped  or  a  fish ;  they  simply 
aimed    at    producing    motion    adapted    to    the    land    and 
water,  in   accordance  with  natural   laws,  and   in  the   pre- 
sence of  living  models.     Their  success  is  to  be  measured  by 
an  involved  labyrinth  of  railway  which   extends  to  every 
part  of  the  civilized  world ;  and  by  navies  whose  vessels  are 
despatched  without  trepidation  to  navigate  the  most  boisterous 
seas  at  the  most  inclement  seasons.      The  aeronaut  has  a 
similar  but  more  difficult  task  to  perform.     In  attempting  to 
produce  a  flying-machine  he   is  not  necessarily  attempting 
an  impossible  thing.     The  countless  swarms  of  flying  crea- 
tures testify  as  to  the  practicability  of  such  an  undertaking, 
and  nature  supplies  him  at  once  with  models  and  materials. 
If  artificial  flight  were  not  attainable,  the  insects,  bats,  and 
birds  would  furnish  the  only  examples  of  animals  whose, 
movements   could   not   be   reproduced.      History,   analogy, 
observation,  and  experiment   are  all  opposed  to  this  view. 
The  success  of  the  locomotive  and  steamboat  is  an  earnest 
of  the  success  of  the  flying  machine.     If  the  difficulties  to 
be  surmounted  in  its  construction  are  manifold,  the  triumph 
and  the  reward  will  be  correspondingly  great.      It  is  impos- 
sible to  over-estimate  the  boon  which  would  accrue  to  mankind 
from  such  a  creation.    Of  the  many  mechanical  problems  before 
the  world  at  present,  perhaps  there  is  none  greater  than  that 
of  aerial  navigation.     Past  failures  are  not  to  be  regarded 
as   the   harbingers  of  future  defeats,  for  it  is  only  within 
the  last  few  years  that   the  subject  of  artificial  flight  has 
been  taken  up  in  a  true  scientific  spirit.      Within   a  c-.nu- 
paratively  brief  period  an  enormous  mass  of  valuable  data 
has  been  collected.     As  societies  for  the  advancement  of  aero- 
nautics have  been  established  in  Britain,  America,  France, 


260 


AERONAUTICS. 


and  other  countries,  there  is  reason  to  believe  that  our 
knowledge  of  this  most  difficult  department  of  science  will 
go  on  increasing  until  the  knotty  problem  is  finally  solved. 
If  this  day  should  ever  come,  it  will  not  be  too  much  to 
affirm,  that  it  will  inaugurate  a  new  era  in  the  history  of 
mankind  ;  and  that  great  as  the  destiny  of  our  race  has  been 
hitherto,  it  will  be  quite  out-lustred  by  the  grandeur  and 
magnitude  of  coming  events. 


INDEX. 

Ma 

AERIAL  creatures  not  stronger  than  terrestrial  ones,       .  .          .       13 

Aerial  flight  as  distinguished  from  sub-aquatic  flight,     .  .  .92 

Aeronautics,  .  *......      209 

Air  cells  in  insects  and  birds  not  necessary  to  flight,       .  .  .115 

Albatross,  flight  of,  compared  to  compass  set  upon  gimbals,      .  .      199 

Amphibia  have  larger  travelling  surfaces  than  land  animals,  but  less 

than  aerial  ones,          .  .  .  ...          8 

Artificial  fins,  flippers,  and  wings,  how  constructed,       .  .  .14 

Artificial  wings,  Borelli,    .......      219 

Do.  Marey,     .......      226 

Do.  Chabrier,  .  .  .  .  .  .233 

Do.  Straus- Durckheim,          .....      233 

Do.  how  to  apply  to  the  air,  ....      245 

Do.  nature  of  forces  required  to  propel,       ...      246 

Artificial  wave  wing  of  Pettigrew,  .  .  .  -    .      236 

Do.  how  to  construct  on  insect  type,  ...  .      240 

Do.  how  to  construct  to  evade  the  superimposed  air  during 

the  up  stroke,  ......       241 

Do.  can  create  currents  and  rise  upon  them,  .  .      253 

Do.  can  be  driven  at  any  speed ;  can  make  new  currents 

and  utilize  old  ones,     ....          251,  255 

Do.  as  a  propeller  and  aerial  screw,  ....      266 

Do.  compound  rotation  of :  the  different  parts  of  the  wing 

travel  at  different  speeds,         ....      252 

Do.  necessity  for  supplying  root  of,  with  elastic  structures,        247 

Artificial  compound  wave  wing  of  Pettigrew,        ....      242 

Atmospheric  pressure,  effects  of,  on  limbs,          .  .  .  .24 

Axioms,  fundamental,        .  .  .  .  .  .  .17 

BALANCING,  how  effected  in  flight,            .....  118 

Balloon, 210 

Bats  and  birds,  lax  condition  of  shoulder-joint  in,          ...  190 

Birds,  lifting  capacity  of,               ....                       .  2<if> 

Body  and  wing  reciprocate  in  flight,  and  each  describes  a  waved  track,  12 

Bones,          .........  21 

Bones  of  the  extremities  twisted  and  spiral,         .  .  .  28,  '.?.< 

Bones  of  wing  of  bat— spiral  configuration  of  their  articular  surfaces,    .  176 

Bones  of  wing  of  bird — their  articular  surfaces,  movements,  etc.,         .  178 

Borelli's  artificial  bird,       .......  220 

CHABRIER'S  artificial  wings,          ....••      233 


262 


INDEX. 


PAGE 

ELYTRA  or  wing  cases  and  membranous  wings,    ....      170 

FEATHERS,  primary,  secondary,  and  tertiary,       .  180 

Fins,  flippers,  and  wings  form  mobile  helices  or  screws,  14 

Flight,  weight  necessary  to,  ...          3,  4,  110  111,  112,  113 

Flight  the  poetry  of  motion,          ....  6 

Flight  the  least  fatiguing  kind  of  motion,             .           .  13 

Flight  under  water,            .....  90 

Flight  of  the  flying-fish,     .....  98 

Flight,  horizontal,  in  part  due  to  weight  of  flying  mass,  110 

Flight — the  regular  and  irregular,              .            .            .  201 

Flight — how  to  ascend,  descend,  and  turn,           .            .  201 

Flight  of  birds  referrible  to  muscular  exertion  and  weight,  204 

Fluids,  mechanical  effects  of,  on  animals  immersed  in  them,  78 

Fluids,  resistance  of,          .                         ...  18 

Flying  machine,  Henson,  .                        ...  212 

Do.            Stringfellow,                    ...  213 

Do.            Cay  ley,    .                        ...  215 

Do.            Phillips,  .                        ...  216 

Do.            M.  de  la  Landelle,           ...  217 

Do.            Borelli,     .                        ...  219 

A  flying  machine  possible,                         ...  2,  3 

Forces  which  propel  the  wings  of  insects,  bats,  and  birds,  186,  189 

Fulcra,  yielding,     ......  8,  104,  165 

GRAVITY,  the  legs  move  by  the  force  of,  .  .  .  .18 

Gravity,  centre  of,  .....  .18 

HISTORY  of  the  figure-of-8  theory  of  walking,  swimming,  and  flying,    .        15 
JOINTS,       .........        23 

KITE-LIKE  action  of  the  wings,      ......        98 

Kite — how  kite  formed  by  wing  differs  from  boy's  kite,  .  .      166 

LAWS  of  natural  and  artificial  progression  the  same,       .           .           .  4,  17 

Legs,  moved  by  the  force  of  gravity,        .....  18 

Lever — the  wing  one  of  the  third  order,    .....  103 

Levers,  the  three  orders  of,            ......  19 

Life  linked  to  motion,        .  .  .  .  .  .  .3 

Lifting  capacity  of  birds,   .......  205 

Ligaments,               ........  24 

Ligaments,  elastic,  position  and  action  of,  in  wing  of  pheasant,  snipe, 

crested  crane,  swan,  etc.,        ......  191 

Ligaments,  elastic,  more  highly  differentiated  in  wings  which  vibrate 

quickly,           .            .            .            .            .            .            .            .  193 

Locomotion,  the  active  organs  of,             .....  24 

Locomotion,  the  passive  organs  of,            .....  21 

Locomotion  of  the  horse,   .  .  ...  .  .  .39 

Locomotion  of  the  ostrich,             .           .           .           .           .          •.  45 

Locomotion  of  man,  .......  51 

MAREY'S  artificial  wings,    .......  233 

Membranous  wings,             .......  170 

Motion  associated  with  the  life  and  well-being  of  animals,         .            .  1 

Motion  not  confined  to  the  animal  kingdom,        ....  2 

Motion,  natural  and  artificial,       ......  4 


INDEX.  263 

Motion,  of  uniform,  .  . 

Motion  uniformly  varied,  . 

Muscles,  their  properties,  mode  of  action,  etc.,    .  24 

Muscles  arranged  iu  longitudinal,  transverse,  and  oblique  spiral  lines, '.        28 

Muscles,  oblique  spiral,  necessary  for  spiral  bones  and  joints,  .            .        81 

Muscles  take  precedence  of  bones  in  animal  movements,  .           .        29 

Muscular  cycles,     ......  26 

Muscular  waves,     .....  26 

PKNDULUMS,  the  extremities  of  animals  act  as,  in  walking,        .    9,  18,  56,  57 
Plane,  inclined,  as  applied  to  the  air,        .....       211 

Pettigrew's  method  of  constructing  and  applying  artificial  wings  as 
contradistinguished  from  that  of  Borelli,  Chabrier,  Durckheim, 
Marey,  etc.,     ........      235 

Pettigrew's  wave  wing,      .......      236 

•Pettigrew's  compound  wave  wing,  .....      242 

Progression  on  the  land,    .  .  .  .  .  .  .37 

Do.        on  or  in  the  water,      ......        64 

Do.   •  in  or  through  the  air,  .....      103 

QUADRUPEDS  walk,  fishes  swim,  and  insects,  bats,  and  birds  fly,  by 

figure-of-8  movements,  .  .  .  .  .  .  15,  16 

SCREWS — the  wing  of  the  bird  and  the  extremity  of  the  biped  and 

quadruped  screws,  structurally  and  functionally,     .  .  .12 

Screws — difference  between  those  formed  by  the  wings  and  those  em- 
ployed in  navigation,  ......      151 

Sculling  action  of  the  wing,  ......       231 

Speed  attained  by  insects,  ......      188 

Speed  of  wing  movements  partly  accounted  for,  .  .  .       120 

Spine,  spiral  movements  of,  transferred  to  the  extremities,        .  .33 

Straus-Durckheim's  artificial  wings,          .....      233 

Swimming  of  the  fish,  whale,  porpoise,  etc.,        .  ...        66 

Swimming  of  the  seal,  sea-bear,  and  walrus,        .  .  .  .74 

Swimming  of  man,  .......        78 

Swimming  of  the  turtle,  triton,  crocodile,  etc.,    .  .  .  .89 

TERRESTRIAL  animals  have  smaller  travelling  surfaces  than  amphibia, 

amphibia  than  fishes,  and  fishes  than  insects,  bats,  and  birds,  .  8 

The  travelling  surfaces  of  animals  increase  as  the  density  of  the  media 

traversed  decreases,  .  .  .  .  .  .  .  7,  8 

The  travelling  surfaces  of  animals  variously  modified  and  adapted  to 

the  media  on  or  in  which  they  move,  .  .  .  .34 

WALKING,  swimming,  and  flying  correlated,        .  .  •  .          5 

Walking  of  the  quadruped,  biped,  etc.,    ....          9,10,11 

Wave  wing  of  Pettigrew,  ..... 

Do.        how  to  construct  on  insect  type,       .•  240 

Do.        how  to  construct  to  evade  the  superimposed  air  during  the 
up  stroke,    ...... 

Do.        can  be  driven  at  any  speed,  ....          251,  255 

Do.         can  create  currents  and  rise  upon  them,       .  . 

Do.        can  make  new  currents  and  utilize  existing  ones,    .          251,  255 

Do.         as  a  propeller,  ...  . 

Do.        as  an  aerial  screw,      .  ... 

Do.         forces  required  to  apply  to  the  air,   .  .  .  245,  24 

Do.        necessity  for  supplying  root  of,  with  elastic  structures,      .      247 


264  INDEX. 

PAGE 

Wave  wing,  compound,      .......       242 

Weight  necessary  to  flight,  ......       110 

Weight  contributes  to  flight,         ......       112 

Weight,  momentum,  and  power  to  a  certain  extent  synonymous  in 

flight, 114 

The  wing  of  the  bird  and  the  extremity  of  the  biped  and  quadruped  are 

screws,  structurally  and  functionally,  ...  12,  138 

Wing  in  flight  describes  figure-of-8  curves,  .  .  .  .12 

Wing  during  its  action  reverses  its  planes  and  describes  a  figure-of-8 

track  in  space,          .......      140 

Wing  when  advancing  with  the  body  describes  looped  and  waved  tracks,      143 
Wing,  margins  of,  thrown  into  opposite  curves  during  extension  and 

flexion,  ........      146 

Wing,  tip  of,  describes  an  ellipse,  .....       147 

Wing  and  body  reciprocate  in  flight,  and  each  describes  a  wave  track,  12 

Wing  moves  in  opposite  curves  to  body,  .  .  .  .168 

Wing  ascends  when  body  descends,  and  vice  versd,          .  .  .      159 

Wing  during  its  vibrations  produces  a  cross  pulsation,    .  .      148 

Wing  vibrates  unequally  with  reference  to  a  given  line,  .  150,  231 

Wing,  compound  rotation  of,  •  .  .  .  .  .      149 

Wing  a  lever  of  the  third  order,    ......      103 

Wing  acts  on  yielding  fulcra,         .  .  .  .  -8,  104,  165 

Wings,  their  form,  etc.,  all  wings  screws,  structurally  and  functionally,        136 
Wing  capable  of  change  of  form  in  all  its  parts,  .  .  .147 

Wing-area  variable  and  in  excess,  .....      124 

Wing-area  decreases  as  the  size  and  weight  of  the  volant  animal  in- 
creases, ;  .....      132 

Wing,  natural,  when  elevated  and  depressed  must  move  forwards,        .      156 
Wing,  angles  formed  by,  when  in  action,  ....       167 

Wing  acts  as  true  kite  both  during  down  and  up  strokes,  .  .       165 

Wing,  traces  of  design  in,  .  .....      180 

Wing  of  bird  not  always  opened  up  to  same  extent  in  up  stroke,  .       182 

Wing,  flexion  of,  necessary  to  flight  of  birds,       .  .  .  .183 

Wing  flexed  and  partly  elevated  by  action  of  elastic  ligaments,  .       191 

Wing,  power  of,  to  what  owing,    .  .....       194 

Wing,  effective  stroke  of,  why  delivered  downwards  and  forwards,        .       195 
Wing  acts  as  an  elevator,  propeller,  and  sustainer  both  during  exten- 
sion and  flexion,          .......       197 

Wings,  points  wherein  the  screws  formed  by,  differ  from  those  in  ordi- 
nary use,          ........       151 

Wings  at  all  times  thoroughly  under  control,      ....       154 

Wings  of  insects,  consideration  of  forces  which  propel,  .  .  .       186 

Wings  of  bats  and  birds,  consideration  of  forces  which  propel,  .  .       189 


LIST  OF  A  UTHORS  AND  SUBJECTS  OF  THEIR  BOOKS, 


TO    BE    PUBLISHED    IN    THE 


INTERNATIONAL  SCIENTIFIC  SERIES. 


Rev.  M.  J.  BERKELEY,  M.  A.,  F.  L.  S., 
and  M.  COOKE,  M.  A.,  LL.  IX,  Fungi; 
their  Nature,  Influences,  and  Uses. 

Prof.  OSCAR  SCHMIDT  (University  of  Stras- 
burg),  The  Theory  of  Descent  and 
Darwinism. 

Prof.  VOGEL  (Polytechnic  Academy  of  Ber- 
lin), The  Chemical  Effects  of  Light. 

Prof.  W.  KINGDOM  CLIFFORD,  M.  A., 
The  First  Principles  of  the  Exact  Sci- 
ences explained  to  the  Non-mathemati- 
cal. 

Prof.  T.  H.  HUXLEY,  LL.  D.,  F.  R.  S., 
Bodily  Motion  and  Consciousness. 

Dr.  W.  B.  CARPENTER,  LL.  D.,  F.  R.  S., 
The  Physical  Geography  of  the  Sea. 

Prof.  WILLIAM  ODLING,  F.  R.  S.,  The  Old 
Chemistry  from  the  New  Stand-point. 

Prof.  SHELDON  AMOS,  The  Science  of  Law. 

W.  LAUDER  LINDSAY,  M.  D.,  F.  R.  S.  E., 
Mind  in  the  Lower  A  nimals. 

Sir  JOHN  LUBBOCK,  Bart.,  F.  R.  S.,  The 
Antiquity  of  Man. 

Prof.  W.  T.  THISELTON  DYER,  B.  A., 
B.  S.  C.,  Form  and  Habit  in  Flower- 
ing Plants. 

Prof.  MICHAEL  FOSTER,  M.  D.,  Proto- 
plasm and  the  Cell  Theory. 

Prof.  W.  STANLEY  JEVONS,  The  Logic  of 
Statistics. 

Dr.  H.  CHARLTON  BASTIAN,  M.D..F.R.S., 
The  Bruin  as  an  Organ  of  Mind. 

Prof.  A.  C.  RAMSAY,  LL.  D.,  P.  R.  S., 
Earth  Sculpture;  Hills,  Valleys, 
Mountains,  Plains,  Rivers,  Lakes; 
how  they  were  Produced,  and  how 
they  have  been  Destroyed. 

Prof.  RUDOLPH  VIRCHOW  (University  of 
Berlin),  Morbid  Physiological  Action. 

Prof.  CLAUDE  BERNARD  (College  of 
France),  Physical  and  Metaphysical 
Phenomena  of  Life. 

Prof.  A.  QUETF.LET  (Brussels  Academy  of 
Sciences),  Social  Physics. 


Prof.  H.  SAINTE-CLAIRE  DEVILLE,  A  n  In- 
troduction to  General  Chemistry. 

Prof.  WURTZ,  Atoms  and  the  Atomic 
Theory. 

Prof.  DE  QUATREFAGES,  The  Negro 
Races. 

Prof.    LACAZE-DUTHIERS,   Zoology   since 

Cu-vier. 
Prof.  BERTHELOT,  Chemical  Synthesis. 

Prof.  J.  ROSENTHAL,  General  Physiology 

of  Muscles  and  Nerves. 
Prof.  C.  A.  YOUNG  (Dartmouth  College), 

The  Sun. 

Prof.  JAMES  D.  DANA,  M.  A.,  LL.  D.,  On 
Cephahzaiion  ;  or,  Head-Character* 
in  the  Gradation  and  Progress  of 

Life. 

Prof.  S.  W.  JOHNSON,  M.  A.,  On  the  Nu- 
trition of  Plants. 

Prof.  AUSTIN  FLINT,  Jr.,  M.  D.,  The  Ner. 
vous  System  and  its  Relation  to  the 
Bodily  Functions. 

Prof.  W.  D.  WHITNEY,  Modern  Linguis- 
tic Science. 

Prof.  BERNSTEIN  (University  of  Halle), 
Physiology  of  the  Senses. 

Prof.  FERDINAND  COHN  (University  of 
Breslau),  Thallotyphes  (Algae  Lichens 
Fungi). 

Prof.  HERMANN  (University  of  Zurich), 
Respiration. 

Prof.  LEUCKART  (University  of  Leipsic), 
Outlines  of  A  nimal  Organization. 

Prof.    LIEBREICH  (University  of  Berlin), 

Outlines  of  Toxicology. 
Prof.    KUNDT   (University  of  Strasburg), 

On  Sound. 
Prof.  LONMEL   (University  of  Erlangen). 

Optics. 
Prof.  REES  (University  of  Erlangen),  On 

Parasitic  Plants. 
Prof.  STEINTHAL  (University  of  Berlin), 

Outlines  of  the  Science  of  Language. 


D.  APPLETON  &  CO.,  Publishers,  $49  &  551  Broadway,  N.  Y. 


Opinions  of  the  Press  on  the  "International  Scientific  Series" 


Tyndall's  Forms  of  Water. 

I  vol.,  I2mo.     Cloth.     Illustrated Price,  $1.50. 

"  In  the  volume  now  published,  Professor  Tyndall  has  presented  a  noble  illustration 
of  the  acuteness  and  subtlety  of  his  intellectual  powers,  the  scope  and  insight  of  his 
scientific  vision,  his  singular  command  of  the  appropriate  language  of  exposition,  and 
the  peculiar  vivacity  and  grace  with  which  he  unfolds  the  results  of  intricate  scientific 
research." — N.  Y.  Tribune. 

"  The  '  Forms  of  Water,'  by  Professor  Tyndall,  is  an  interesting  and  instructive 
little  volume,  admirably  printed  and  illustrated.  Prepared  expressly  for  this  series,  it 
is  in  some  measure  a  guarantee  of  the  excellence  of  the  volumes  that  will  follow,  and  an 
indication  that  the  publishers  will  spare  no  pains  to  include  in  the  series  the  freshest  in- 
vestigations of  the  best  scientific  minds." — Boston  Journal. 

"This  series  is  admirably  commenced  by  this  little  volume  from  the  pen  of  Prof. 
Tyndall.  A  perfect  master  of  his  subject,  he  presents  in  a  style  easy  and  attractive  his 
methods  of  investigation,  and  the  results  obtained,  and  gives  to  the  reader  a  clear  con- 
ception of  all  the  wondrous  transformations  to  which  water  is  subjected." — Churchman. 


II. 

Bagehot's  Physics  and  Politics. 

I  vol.,  I2mo.     Price,  $1.50. 

"  If  the  '  International  Scientific  Series '  proceeds  as  it  has  begun,  it  will  more  than 
fulfil  the  promise  given  to  the  reading  public  in  its  prospectus.  The  first  volume,  by 
Professor  Tyndall,  was  a  model  of  lucid  and  attractive  scientific  exposition  ;  and  now 
we  have  a  second,  by  Mr.  Walter  Bagehot,  which  is  not  only  very  lucid  and  charming, 
but  also  original  and  suggestive  in  the  highest  degree.  Nowhere  since  the  publication 
of  Sir  Henry  Maine's  'Ancient  Law,'  have  we  seen  so  many  fruitful  thoughts  sug- 
gested in  the  course  of  a  couple  of  hundred  pages.  .  .  .  To  do  justice  to  Mr.  Bage- 
hot's fertile  book,  would  require  a  long  article.  With  the  best  of  intentions,  we  are 
conscious  of  having  given  but  a  sorry  account  of  it  in  these  brief  paragraphs.  But  we 
hope  we  have  said  enough  to  commend  it  to  the  attention  of  the  thoughtful  leader." — 
Prof.  JOHN  FISKE,  in  the  Atlantic  Monthly. 

"  Mr.  Bagehot's  style  is  clear  and  vigorous.  We  refrain  from  giving  a  fuller  ac- 
count of  these  suggestive  essays,  only  because  we  are  smre  that  our  readers  will  find  it 
worth  their  while  to  peruse  the  book  for  themselves ;  and  we  sincerely  hope  that  the- 
forthcoming  parts  of  the  'International  Scientific  Series'  will  be  as  interesting."— 
A  thenteum. 

"  Mr.  Bagehot  discusses  an  immense  variety  of  topics  connected  with  the  progress 
of  societies  and  nations,  and  the  development  of  their  distinctive  peculiarities;  and  his 
book  shows  an  abundance  of  ingenious  and  original  thought" — ALFRED  RUSSKH 
WALLACE,  in  Nature. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y. 


Opinions  of  the  Press  on  the  "International  Scientific  Series" 

III. 

Foods. 

By   Dr.  EDWARD   SMITH. 
I  vol.,  I2mo.     Cloth.     Illustrated p,.jce   «j  _. 

In  ma'cing  up  THE  INTERNATIONAL  SCIENTIFIC  SERIES,  Dr.  Edward  Smith  was  se- 
lected as  the  ablest  man  in  England  to  treat  the  important  subject  of  Foods.  His  services 
were  secured  for  the  undertaking,  and  the  little  treatise  he  has  produced  shows  that  the 
choice  of  a  writer  on  this  subject  was  most  fortunate,  as  the  book  is  unquestionably  the 
clearest  and  best-digested  compend  of  the  Science  of  Foods  that  has  appeared  in  our 
language. 

"  The  book  contains  a  series  of  diagrams,  displaying  the  effects  of  sleep  and  meals 
on  pulsation  and  respiration,  and  of  various  kinds  of  food  on  respiration,  which  as  the 
results  of  Dr.  Smith's  own  experiments,  possess  a  very  high  value.  We  have'not  far 
to  go  in  this  work  for  occasions  of  favorable  criticism  ;  they  occur  throughout  but  are 
perhaps  most  apparent  in  those  parts  of  the  subject  «ith  which  Dr.  Smith's  name  is  es- 
pecially linked.  — London  Examiner. 

"The  union  of  scientific  and  popular  treatment  in  the  composition  of  this  work  will 
afford  an  attraction  to  many  readers  who  would  have  been  indifferent  to  purely  theoreti- 
cal details.  .  .Still  his  work  abounds  in  information,  much  of  which  is  of  great  value, 
and  a  part  of  which  could  not  easily  be  obtained  from  other  sources.  Its  interest  is  de- 
cidedly  enhanced  for  students  who  demand  both  clearness  and  exactness  of  statement, 
by  the  profusion  of  well-executed  woodcuts,  diagrams,  and  tables,  which  accompany  th« 
volume.  .  .  The  suggestions  of  the  author  on  the  use  of  tea  and  coffee,  and  of  the  va. 
nous  forms  of  alcohol,  although  perhaps  not  strictly  of  a  novel  character,  are  highly  in- 
structive,  and  form  an  interesting  portion  of  the  volume." — N.  Y.  Tribune. 

IV. 

Body  and  Mind. 

THE    THEORIES   OF   THEIR    RELATION. 

By   ALEXANDER    BAIN,    LL.  D. 
I  vol.,    I2mo.      Cloth Price,  $1.50. 

PROFESSOR  BAIN  is  the  author  of  two  well-known  standard  works  upon  the  Science 
of  Mind — "The  Senses  and  the  Intellect,"  and  "The  Emotions  and  the  Will."  He  is 
one  of  the  highest  living  authorities  in  the  school  which  holds  that  there  can  be  no  sound 
or  valid  psychology  unless  the  mind  and  the  body  are  studied,  as  they  exist,  together. 

"  It  contains  a  forcible  statement  of  the  connection  between  mind  and  body,  study- 
ing their  subtile  interworkings  by  the  light  of  the  most  recent  physiological  investiga- 
tions. The  summary  in  Chapter  V.,  of  the  investigations  of  Dr.  Lionel  Beale  of  the 
embodiment  of  the  intellectual  functions  in  the  cerebral  system,  will  be  found  the 
freshest  and  most  interesting  part  of  his  book.  Prof.  Bain's  own  theory  of  the  c<  nrix- 
tion  between  the  mental  and  the  bodily  part  in  man  is  stated  by  himself  to  be  as  foil.  \\ :  : 
There  is  '  one  substance,  with  two  sets  of  properties,  two  sides,  the  physical  and  the 
mental — a  double-faced  unity.'  While,  in  the  strongest  manner,  asserting  the  i:nion 
of  mind  with  brain,  he  yet  denies  'the  association  of  union  in  place'  but  asserts  tl-e 
union  of  close  succession  in  time,'  holding  that  'the  same  being  is,  by  alternate  fits,  un- 
der extended  and  under  unextended  consciousness."  ' — Christian  Register. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y. 

^^ 


Opinions  of  the  Press  on  the  "International  Scientific  Series." 


V. 

The  Study  of  Sociology. 

By  HERBERT   SPENCER. 

I2mo.     Cloth Price,  $1.50. 

"The  Study  of  Sociology  "  was  written  for  the  purpose  of  conveying  to  the  reading 
public  more  definite  ideas  concerning  the  nature,  claims,  scope,  limits,  and  difficulties, 
of  the  Science  of  Sociology.  It  is  intended  to  prepare  the  way  for  the  author's  great 
work  on  the  "  Principles  of  Sociology,"  which  is  to  follow  the  "  Principles  of  Psychol- 
ogy." But,  while  serving  thus  as  an  introduction  to  the  larger  work,  the  present  vol- 
ume is  complete  in  itself.  Its  style  is  exceedingly  clear  and  vigorous,  and  the  book 
abounds  with  a  wealth  of  illustration. 

"  The  philosopher  whose  distinguished  name  gives  weight  and  influence  to  this  vol- 
ume, has  given  in  its  pages  some  of  the  finest  specimens  of  reasoning  in  all  its  forms 
and  departments.  There  is  a  fascination  in  his  array  of  facts,  incidents,  and  opinions, 
which  draws  on  the  reader  to  ascertain  his  conclusions.  The  coolness  and  calmness  of 
his  treatment  of  acknowledged  difficulties  and  grave  objections  to  his  theories  win  for 
him  a  close  attention  and  sustained  effort,  on  the  part  of  the  reader,  to  comprehend,  fol- 
low, grasp,  and  appropriate  his  principles.  This  book,  independently  of  its  bearing 
upon  sociology,  is  valuable  as  lucidly  showing  what  those  essential  characteristics  are 
which  entitle  any  arrangement  and  connection  of  facts  and  deductions  to  be  called  a 
tcience." — Episcopalian. 

"To  those  who  are  already  acquainted  with  Mr.  Spencer's  writing,  there  is  no  need 
of  recommending  the  work ;  to  those  who  are  not,  we  would  say,  that  by  reading  '  The 
Study  of  Sociology '  they  will  gain  the  acquaintance  of  an  author  who,  for  knowledge, 
depth  of  thought,  skill  in  elucidation,  and  originality  of  ideas,  stands  prominently  for- 
ward in  the  front  rank  of  the  glorious  army  of  modern  thinkers.  '  The  Study  of  Soci- 
ology'  is  the  fifth  of  '  The  International  Scientific  Series,"  and  for  beauty  of  type  and 
elegant  appearance  is  worthy  of  the  great  publishing-house  of  Messrs.  Appleton&Co." 
—Boston  Gazette. 

"This  volume  belongs  to  'The  International  Scientific  Series,'  which  was  projected 
with  so  high  a  standard  and  which  is  being  so  successfully  carried  out.  The  value  and 
character  of  the  whole  may  fairly  be  judged  by  this  and  the  preceding  volumes.  The 
principle  of  the  enterprise  is  that  eich  subject  shall  be  treated  by  the  writer  of  greatest 
eminence  in  that  department  of  inquiry,  and  it  is  well  illustrated  in  the  present  work. 
Herbert  Spencer  is  unquestionably  the  foremost  living  thinker  in  the  psychological  and 
sociological  fields,  and  this  volume  is  an  important  contribution  to  the  science  of  which 

it  treats It  will  prove  more  popular  than  any  of  its  author's  other  creations,  for 

it  is  more  plainly  addressed  to  the  people  and  has  a  more  practical  and  less  speculative 
cast  It  will  require  thought,  but  it  is. well  worth  thinking  about" — Albany  Evening 
Journal. 

"Whether  the  reader  agrees  with  the  author  or  not,  he  will  be  delighted  with  the 
work,  not  only  for  the  beauty  and  purity  of  its  style,  and  breadth  and  cyclopedic  char- 
acter of  Mr.  Spencer's  mind,  but  also  for  its  freedom  from  prejudice  and  kindred  imper- 
fections."— Norwich  Bulletin. 

"This  work  compels  admiration  by  the  evidence  which  it  gives  of  immense  re- 
search, study,  and  observation,  and  is  withal  written  in  a  popular  and  very  pleasing 
ityle.  It  is  a  fascinating  work,  as  well  as  one  of  deep  practical  thought." — Boston  Pott. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y. 


Opinions  of  the  Press  on  the  "  International  Scientific  Series." 

VI. 

The   New  Chemistry. 

By  JOSIAH  P.  COOKE,  JR., 

Erving  Professor  of  Chemistry  and  Mineralogy  in  Harvard  University. 
I  vol.,   121110.     Cloth Price,  $2.00. 

"  The  book  of  Prof.  Cooke  is  a  model  of  the  modern  popular  science  work.  It  has 
just  the  due  proportion  of  fact,  philosophy,  and  true  romance,  to  make  it  a  fascinating 
companion,  either  for  the  voyage  or  the  study." — Daily  Graphic. 

"  This  admirable  monograph,  by  the  distinguished  Erving  Professor  of  Chemistry 
in  Harvard  University,  is  the  first  American  contribution  to  '  The  International  Scien- 
tific Series,'  and  a  more  attractive  piece  of  work  in  the  way  of  popular  exposition  upon 
a  difficult  subject  has  not  appeared  in  a  long  time.  It  not  only  well  sustains  the  char- 
acter of  the  volumes  with  which  it  is  associated,  but  its  reproduction  in  European  coun- 
tries will  be  an  honor  to  American  science.  It  is,  moreover,  in  an  eminent  degree, 
timely,  for,  between  the  abandonment  of  its  old  views  and  the  bewilderment  caused 
by  the  new,  chemical  science  was  getting»into  a  demoralized  condition.  A  v.  oik  was 
greatly  needed  that  should  relieve  the  discomfort  of  transition,  and  bridge  over  the 
gulf  between  the  old  order  of  ideas  and  those  which  are  to  succeed  them.  Professor 
Cooke's  compendious  contribution  to  the  present  exigencies  of  chemical  literature  will 
give  the  students  of  the  science  exactly  the  help  they  need,  and  pass  them  over  by  an 
easy  and  pleasant  route  into  the  new  realm  of  chemical  philosophy." — New  York 
Tribune. 

"  All  the  chemists  in  the  country  will  enjoy  its  perusal,  and  many  will  seize  upon  it 
as  a  thing  longed  for.  For,  to  those  advanced  students  who  have  kept  well  abreast  of 
the  chemical  tide,  it  offers  a  calm  philosophy.  To  those  others,  youngest  of  the  class, 
who  have  emerged  from  the  schools  since  new  methods  have  prevailed,  it  presents  a 
generalization,  drawing  to  its  use  all  the  data,  the  relations  of  which  the  newly-fledged 
fact-seeker  may  but  dimly  perceive  without  its  aid.  ...  To  the  old  chemists.  Prof. 
Cooke's  treatise  is  like  a  message  from  beyond  the  mountain.  They  have  heard  of 
changes  in  the  science ;  the  clash  of  the  battle  of  old  and  new  theories  has  stirred  them 
from  afar.  The  tidings,  too,  had  come  that  the  old  had  given  way ;  and  little  more  than 
this  they  knew.  .  .  .  Prof.  Cooke's' New  Chemistry '  must  do  wide  service  in  bringing 
to  close  sight  the  little  known  and  the  longed  for.  ...  As  a  philosophy  it  is  elemen- 
tary, but,  as  a  book  of  science,  ordinary  readers  will  find  it  sufficiently  advanced." — 
Utica  Morning  Herald. 

"A  book  of  much  higher  rank  than  most  publications  of  its  class.  It  treats  only 
of  modern  chemical  theories — relating  to  molecules,  combining  proportions,  reactions 
atomic  weights,  isomerism,  and  the  synthesis  of  organic  compounds — taking  one  into 
the  very  arcana  of  chemical  mysteries.  Though  there  are  no  more  recondite  btanches 
of  the  science  than  those  here  explained  and  illustrated,  such  is  Professor  Cooke's 
clearness  that  he  may  be  said  to  make  every  thing  plain  _to  the  average  reader,  who 
will  hut  take  pains  with  his  lessons.  Professor  Cooke  reminds  us.  in  his  simplicity  and 
lucidity  of  statement,  of  Professor  Tyndall,  than  which  there  can  be  no  higher  praise." 
—New  York  Journal  of  Commerce. 

"  The  aim  of  the  work  is  to  furnish  a  hand-book  of  a  symmetrical  science,  resting 
fundamentally  upon  the  law  of  Avogadro  that  '  equal  volumes  of  all  substances,  when 
in  the  state  of  gas  and  under  like  conditions,  contain  the  same  number  of  molecules.' 
It  is  to  a  rigid  adherence  to  this  law  and  the  deductions  which  flow  from  it  that  chem- 
istry, as  now  taught,  owes  the  marked  difference  which  separates  it  from  the  chemistry 
taught  a  few  years  ago.  The  original  lectures  of  Professor  Cooke,  enlarged  and 
somewhat  modified,  present  in  their  present  form  a  clear  and  full  exposition  of  the  sci- 
ence, and  will  form  a  useful  text-book  as  well  as  a  volume  of  unusual  interest  to  the 
lovers  of  physical  science."— New  York  ll'orld. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y. 


Opinions  of  the  Press  on  the  "  International  Scientific  Series." 

VII. 

The  Conservation  of  Energy. 

By  BALFOUR   STEWART,  ~LL.  D. 

With  an  Appendix,  treating  of  the  Vital  and  Mental  Applications  of 

the  Doctrine. 
I  vol.,  I2mo.     Cloth Price,  $1.50. 

Note  to  the  A  merican  Edition. 

"The  great  prominence  which  the  modern  doctrine  of  the  Conservation  of  Energy 
or  Correlation  of  Forces  has  lately  assumed  in  the  world  of  thought,  has  made  a  simple 
and  popular  explanation  of  the  subject  very  desirable.  The  present  work  of  Di.  1  al- 
four  Stewart,  contributed  to  the  'International  Scientific  Series,' fully  meets  this  re- 
quirement, as  it  is  probably  the  clearest  and  most  elementary  statement  of  the  question 
that  has  yet  been  attempted.  Simple  in  language,  copious  and  familiar  in  illusti alien, 
and  remarkably  lucid  in  the  presentation  of  facts  and  principles,  his  little  treatise  forms 
just  the  introduction  to  the  great  problem  of  the  interaction  of  natural  foices  that  is  re- 
quired by  general  readers.  But  Prof.  Stewart  having  confined  himself  mainly  to  the 
physical  aspects  of  the  subject,  it  was  desirable  that  his  views  should  be  supplemented 
by  a  statement  of  the  operation  of  the  principle  in  the  spheres  of  life  and  mind.  An 
Appendix  has,  accordingly,  been  added  to  the  American  edition  of  Dr.  Stewart's 
work,  in  which  these  applications  of  the  law  are  considered. 

"  Prof.  Joseph  Le  Cpnte  published  a  very  able  essay  fourteen  years  ago  on  the 
'Correlation  of  the  Physical  and  Vital  Forces,'  which  was  extensively  reprinted  abro?d, 
and  placed  the  name  of  the  author  among  the  leading  interpieters  of  the  subject.  His 
mode  of  presenting  it  was  regarded [as  peculiaily  happy,  and  was  widely  adopted  by  other 
writers.  After  further  investigations  and  more  mature  reflection,  he  has  recently  re- 
stated his  views,  and  has  kindly  furnished  the  revised  essay  for  insertion  in  this  volun.e. 

"  Prof.  A.  Bain,  the  celebrated  Psychologist  cf  Aberdeen,  who  has  done  so  much 
to  advance  the  study  ofmind  in  its  physiological  relations,  prepared  an  interesting  lec- 
ture not  long  ago  on  the  'Correlation  of  the  Nervous  and  Mental  Forces,'  \\hich  v  ?s 
read  with  much  interest  at  the  time  of  its  publication,  and  is  now  reprinted  as  a  suiti.ble 
exposition  of  that  branch  of  the  subject.  These  two  essays,  by  carrying  out  the  prin- 
ciple .in  the  field  of  vital  and  mental  phenomena,  will  serve  to  give  completeness  and 
much  greater  value  to  the  present  volume." 

"  The  great  physical  generalization  called  '  The  Conservation  of  Energy '  is  in  «n 
intermediate  state.  It  is  so  new  that  all  kinds  of  false  ideas  are  prevalent  shout  it;  it 
is  so  exact  that  these  cannot  be  tolerated  ;  and  thus  its  circumstances  are  such  as  to 
make  so  thorough  and  simple  a  treatise  as  this,  by  Prof.  Balfour  Stewart,  a  boon  to 
science  anil  the  world  at  large. 

"  The  scheme  of  the  book  is  simple,  as  is  naturally  the  ca=e  when  the  subject-mat- 
ter comprehends  but  one  single  law  of  Nature  and  its  manifestations.  The  first  two 
chapters  are  devoted  to  the  consideration  of  mechanical  energy  and  its  change  into 
heat,  Prof.  Stewart  rightly  devoting  special  attention  to  these  two  forms  of  eneigy, 
compared  with  which  all  others  are  insignificant  in  practical,  if  not  in  theoretical,  im- 
portance. The  remaining  forms  of  energy  are  then  explained,  and  the  law  of  its  con- 
servation is  stated,  and  its  operation  traced  through  all  varieties  of  transmutations.  An 
historical  sketch  of  the  progress  of  the  science  and  an  examination  of  Prof.  Thomson's 
correlative  theory  of  the  'Dissipation  of  Energy  '  follow  ;  and  the  work  cor  eludes  with 
a  chapter  on  the  '  Position  of  Life,'  which  is  closely  connected  with  a  well-known  e«;  y 
written  some  years  ago  by  Prot  Stewart  and  Mr.  I.rckyer.  The  style  is  all  that  it 
should  be;  it  is  difficult  to  understand  how  so  much  information  can  be  contained  in  ro 
few  words.  Prof.  Stewart  could  not  have  been  nearly  so  successful  in  this  rrspect  hrd 
he  been  in  any  degree  a  pedant.  No  such  writer  would  permit  himself  to  use  the 
quaint  language  and  still  quainter  similes  and  and  illustrations  that  make  the  book  f  o 
readable,  and  yet  there  is  Vcarcely  one  that  is  out  of  place,  or  illegitimately  used,  or 
likely  to  mislead." — Saturday  Review. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y. 


A  thoughtful  and  valuable  contribution  to  the  best  religious  literature 
of  the  day. 

RELIGION  AND  SCIENCE. 

A  Series  of  Sunday  Lectures  on  the  Relation  of  Natural  and  Revealed 
Religion,  or  the  Truths  revealed  in  Nature  and  Scripture. 

By  JOSEPH    LE    CONTE, 

PROFE8SOB   OP   GEOLOGY   AND   NATURAL   UI8TOBY   IN   THE   UNIVERSITY    OF  CALIFORNIA. 

I2nio,  cloth.     Price,  $1.50. 

OPINIONS    OF   THE   PRESS. 

"  This  work  is  chiefly  remarkable  as  a  conscientious  effort  to  reconcile 
the  revelations  of  Science  with  those  of  Scripture,  and  will  be  very  use- 
ful to  teachers  of  the  different  Sunday-schools." — Detroit  Union. 

"It  will  be  r.een,  by  this  resttme  of  the  topics,  that  Prof.  Le  Conte 
grapples  with  some  of  the  gravest  questions  which  agitate  the  thinking 
world.  He  treats  of  them  all  with  dignity  ar.d  fairness,  and  in  a  man- 
ner so  clear,  persuasive,  and  eloquent,  as  to  engage  the  undivided  at- 
tention of  the  reader.  We  commend  the  book  cordially  to  then  grid 
of  all  who  are  interested  in  whatever  pertains  to  the  discussion  of  tnc.'e 
grave  questions,  and  especially  to  those  who  desire  to  examine  clcstly 
the  strong  foundations  on  which  the  Christian  faith  is  reared." — Bcstm 
Journal. 

"A  reverent  student  of  Nature  and  religion  is  the  best-qualified  rr.rn 
to  instruct  others  in  their  harmony.  The  author  at  first  intcncUd  l.is 
work  for  a  Bible-class,  but,  as  it  grew  under  his  hands,  it  seemed  v  1 11  to 
give  it  form  in  a  neat  volume.  The  lectures  are  from  a  decidedly  re- 
ligious stand-point,  and  as  such  present  a  new  method  of  treatn  int." 
— Philadelphia  Age. 

"This  volume  is  made  up  of  lectures  delivered  to  his  pupils,  and  is 
written  with  much  clearness  of  thought  and  unusual  clearness  of  ex- 
pression, although  the  author's  English  is  not  always  above  reproach. 
It  is  partly  a  treatise  on  natural  theology  and  partly  a  defense  of  the 
Bible  against  the  assaults  of  modern  science.  In  the  latter  aspect  the 
author's  method  is  an  eminently  wise  one.  He  accepts  whatever  sci- 
ence has  proved,  and  he  also  accepts  the  divine  origin  of  the  Fille. 
Where  the  two  seem  to  conflict  he  prefers  to  await  the  reconcilint;<  r, 
which  is  inevitable  if  both  are  true,  rather  than  to  waste  time  and  wins 
in  inventing  ingenious  and  doubtful  theories  to  force  them  into  sccn.irg 
accord.  Both  a>  a  theologian  and  a  man  of  science,  Prof.  Le  Conte's 
opinions  are  entitled  to  respectful  attention,  and  there  are  few  \\ho  vill 
not  recognize  his  book  as  a  thoughtful  and  valuable  contribution  to  the 
best  religious  literature  of  the  day." — New  York  World. 

D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y. 


DESCRIPTIVE    SOCIOLOGY. 


MB.  HERBERT  SPENCER  has  been  for  several  years  engaged,  with  the  aid  of 
three  educated  gentlemen  in  his  employ,  in  collecting  and  organizing  the  facts 
concerning  all  orders  of  human  societies,  which  must  constitute  the  data  of  a  true 
Social  Science.  He  tabulates  these  facts  so  as  conveniently  to  admit  of  ex- 
tensive comparison,  and  gives  the  authorities  separately.  He  divides  the  races 
of  mankind  into  three  great  groups :  the  savage  races,  the  existing  civilizations, 
and  the  extinct  civilizations,  and  to  each  he  devotes  a  series  of  works.  The 
first  installment, 

THE  SOCIOLOGICAL  HISTORY  OF  ENGLAND, 

in  seven  continuous  tables,  folio,  with  seventy  pages  of  verifying  text,  is  now 
ready.  This  work  will  be  a  perfect  Cyclopaedia  of  the  facts  of  Social  Science, 
independent  of  all  theories,  and  will  be  invaluable  to  all  interested  in  social 
problems.  Price,  five  dollars.  This  great  work  is  spoken  of  as  follows : 

From  the  British  Quarterly  Review. 

"No  words  are  needed  to  indicate  the  immense  labor  here  bestowed,  or  the  great 
sociological  benefit  which  such  a  mass  of  tabulated  matter  done  under  each  competent 
direction  will  confer.  The  work  will  constitute  an  epoch  in  the  science  of  comparative 
sociology." 

From  the  Saturday  Review. 

"  The  plan  of  the  '  Descriptive  Sociology '  is  new,  and  the  task  is  one  eminently  fitted 
to  be  dealt  with  by  Mr.  Herbert  Spencer's  faculty  of  scientific  organizing.  His  object  is 
to  examine  the  natural  laws  which  govern  the  development  of  societies,  as  be  has  ex- 
amined in  formei  parts  of  his  system  those  which  govern  the  development  of  individual 
life.  Now,  it  is  obvious  that  the  development  of  societies  can  be  studied  only  in  their 
history,  and  that  general  conclusions  which  shall  hold  good  beyond  the  limits  of  particu- 
lar societies  cannot  be  safely  drawn  except  from  a  very  wide  range  of  facts.  Mr.  Spen- 
cer has  therefore  conceived  the  plan  of  making  a  preliminary  collection,  or  perhaps  we 
should  rather  say  abstract,  of  materials  which  when  complete  will  be  a  classified  epi- 
tome of  nnive  sal  history." 

From  the  London  Examiner. 

"Of  the  treatment,  in  the  main,  we  cannot  speak  too  highly;  and  we  must  accept 
It  as  a  wonderfully  successful  first  attempt  to  furnish  the  student  of  social  science  with 
data  standing  toward  his  conclusions  in  a  relation  like  that  in  which  accounts  of  the 
structures  and  functions  of  different  types  of  animals  stand  to  the  conclusions  of  th« 
biologist." 


-ies9482 


S  c  IE  NTiFic  SERIES  |  Cu 


